do anything you can reliably stick to. it doesn't matter if you have The Perfect Routine™ if you hate it and never do it.

any combination of pulling, pushing, or lifting exercises will work out the muscle groups you're looking for (pull-ups and push-ups being the easiest and most notable). if you have access for some reason (live near the equator?) swimming is a phenomenal workout for getting a lean and cut upper body (and it's also fun!!!)

for resources check out musclewiki. also, margaret killjoy just put out a great episode on all-around fitness for people who aren't already greek gods

Bodyweight fitness routines are great if you don't want to buy a lot of equipment or go to the gym (doubly so during covid). A lot of the exercises can be done with stuff around the house, and at the most you need a cheap pull-up bar and set of rings. The exercises also naturally adapt to different levels of difficulty, so it's easy for beginners to get started. The recommended routine on reddit is decent.

How fit are you currently and how much do you workout in general? For general getting in shape you will have to keep an eye on how much you eat, have a general idea of calories, and... there is no going around that.

Besides this - for general fitness have a look at the Couch to 5k in the sidebar.

Lifting is always a good idea, but for that I can't really give you advice, and would hope some of the other folks around here provides.