The best way I found when I was first learning was to start by listening to a song and just trying to play the root note along with the chord changes.

Wagon wheel is a great song for this because there’s no unusual chord shapes, and it’s good one to throw out any time says “hey, don’t you play guitar?” just follow the song to try and find the root notes of each chord as their played. This will help you get the rhythm down too.

Noodle around until you’ve got those, and then start playing the major or minor chord shapes instead of just the root. If you’ve got a little music theory, or even just know the chords in the key, this’ll be a little easier. But you should be able to figure out whether the chord should be major or minor by ear. For a lot of songs, this’ll get you reasonably close.

Repeat with a few easier campfire classics, and you’ll start to get a feel for it, which will make more complex songs a little easier. You’re gonna get frustrated every now and then when you come across a chord you’re not used to or a weird chord shape, so feel free to look stuff up if you’re really stuck and can’t figure out after a solid effort. After a while you get better at spotting 7 chords or inversions, but when you’re starting out, just get as close as you can and then if you have to, it’s fine to cheat a little with tabs to get that last 10 percent. After enough practice you’ll find you don’t need to “cheat” quite so often

I used to practice this intentionally a lot more, but nowadays to keep sharp, I sit and noodle while I’m watching tv, and I’ll try to figure out what sounds good over the soundtrack, which is a sorta halfassed way to practice but still give you a feel for figuring out the key of random songs, which helps for learning things by ear.

Lmk if you’ve got any specific questions!