Get or trial Reaper as your daw if you don't already have one (I found Reaper very user friendly and intuitive however any will work) and obtain some vsti's of your choosing, I started with ufo ze.
If you like synthwork then here's a video I used to try and understand them a bit more, it's old and long so there's probably better out there: https://www.youtube.com/watch?v=atvtBE6t48M
If not most synth vsti's have presets and you could always obtain orchestra vsti's, etc so you don't have to fiddle with making a sound.
http://openmusictheory.com/contents.html is a good source I go back to and there's a lot on youtube. After that it depends on how far you want to go.
For starting you just need to understand scales, chords, and progressions. All the white keys on a (virtual) keyboard are apart of C major. Most midi editors should have a piano roll appearance that displays the keys on the left making it very easy to plot a specific note where you want it. Scales are just a series of notes you use and from which chords are created from. For now, just think of them as having 7 unique notes. The C major scale starts at C and ends with B. Within that scale are other scales, or modes, that you can use instead, like using A minor just means you start at A and end at G.
Chords start as a triad which just means three notes -the root note or 1, followed by the third, and then the fifth ( 1, 3, 5) - relative to your root. So a C chord in the scale C major (no black keys, which are sharps/flats; if we are looking for the chords in a scale we will only use the notes of that scale) would be C, which is the root; then its 3rd would be the third note counting from C ( C to D then E, skip the black keys since they are not in C major) so E; and then the fifth would be five from C, so G. So a C major chord would be C, E, G.
The next chord would be D, F, A, which is a D minor chord. The difference between a minor and Major chord is how many intervals are between the root and its third. For now, just know that in a Major scale, the chords created from the first, fourth, and fifth notes are Major (so in C major's case it'd be C major, F major, and G major). The chords created from the second, third, and sixth notes are minor (D minor, E minor, and A minor). The chord created from the seventh note is unique and generally called a diminished a chord: it is B, D, and F. It is called diminished instead of minor because it has a flatted fifth however you probably won't need to worry about that for now.
For chord progressions learning the chord substitution groupings helped me a lot: https://lotusmusic.com/lm_chordsub.html - It's halfway down the page, the little chart with Tonic, subdominant, and dominant on the left. Generally, a chord progression starts with whatever you decide the root chord is, then proceeds to go to the subdominant category (either the chord built off of the second or fourth note), and finally ends in the dominant category (the fifth and seventh chord). Don't view this as an absolute, concrete, requirement however, it's just a very good guideline. One of the most common jazz progressions is 2 - 5 - 1 and probably the most popular pop progression is 1 - 4 - 5.
The chords are grouped into categories that fill similar roles and allow you swap them out without changing the feel of the song too much, which makes sense if you look at the notes they are composed of. In the last link, there is another picture below that chart that shows it pretty well but they are using seventh chords which just means the chord is composed of four notes, with the last note being the note just before the root. I was going to show it here with just triads but I couldn't get it to format correctly. You could try this for yourself by making any progression that ends with the chord built off the fifth note, then replace the fifth chord with the chord built off the seventh note. Now, replace it with the chord built off the fourth note and you should hear the difference, especially if you have them playing back to back. The first two should have the same sort of strong-resolving sound and the third should sound a bit different.
Get or trial Reaper as your daw if you don't already have one (I found Reaper very user friendly and intuitive however any will work) and obtain some vsti's of your choosing, I started with ufo ze.
If you like synthwork then here's a video I used to try and understand them a bit more, it's old and long so there's probably better out there: https://www.youtube.com/watch?v=atvtBE6t48M
If not most synth vsti's have presets and you could always obtain orchestra vsti's, etc so you don't have to fiddle with making a sound.
http://openmusictheory.com/contents.html is a good source I go back to and there's a lot on youtube. After that it depends on how far you want to go.
For starting you just need to understand scales, chords, and progressions. All the white keys on a (virtual) keyboard are apart of C major. Most midi editors should have a piano roll appearance that displays the keys on the left making it very easy to plot a specific note where you want it. Scales are just a series of notes you use and from which chords are created from. For now, just think of them as having 7 unique notes. The C major scale starts at C and ends with B. Within that scale are other scales, or modes, that you can use instead, like using A minor just means you start at A and end at G.
Chords start as a triad which just means three notes -the root note or 1, followed by the third, and then the fifth ( 1, 3, 5) - relative to your root. So a C chord in the scale C major (no black keys, which are sharps/flats; if we are looking for the chords in a scale we will only use the notes of that scale) would be C, which is the root; then its 3rd would be the third note counting from C ( C to D then E, skip the black keys since they are not in C major) so E; and then the fifth would be five from C, so G. So a C major chord would be C, E, G.
The next chord would be D, F, A, which is a D minor chord. The difference between a minor and Major chord is how many intervals are between the root and its third. For now, just know that in a Major scale, the chords created from the first, fourth, and fifth notes are Major (so in C major's case it'd be C major, F major, and G major). The chords created from the second, third, and sixth notes are minor (D minor, E minor, and A minor). The chord created from the seventh note is unique and generally called a diminished a chord: it is B, D, and F. It is called diminished instead of minor because it has a flatted fifth however you probably won't need to worry about that for now.
For chord progressions learning the chord substitution groupings helped me a lot: https://lotusmusic.com/lm_chordsub.html - It's halfway down the page, the little chart with Tonic, subdominant, and dominant on the left. Generally, a chord progression starts with whatever you decide the root chord is, then proceeds to go to the subdominant category (either the chord built off of the second or fourth note), and finally ends in the dominant category (the fifth and seventh chord). Don't view this as an absolute, concrete, requirement however, it's just a very good guideline. One of the most common jazz progressions is 2 - 5 - 1 and probably the most popular pop progression is 1 - 4 - 5.
The chords are grouped into categories that fill similar roles and allow you swap them out without changing the feel of the song too much, which makes sense if you look at the notes they are composed of. In the last link, there is another picture below that chart that shows it pretty well but they are using seventh chords which just means the chord is composed of four notes, with the last note being the note just before the root. I was going to show it here with just triads but I couldn't get it to format correctly. You could try this for yourself by making any progression that ends with the chord built off the fifth note, then replace the fifth chord with the chord built off the seventh note. Now, replace it with the chord built off the fourth note and you should hear the difference, especially if you have them playing back to back. The first two should have the same sort of strong-resolving sound and the third should sound a bit different.
I'm not a professional.