You want a good balance of protein and to minimize carbs, even if carbs are some of the easiest and cheapest foods to buy.
Chicken is the GOAT for good, cheap protein. Buy those breasts and thighs in bulk, freeze em up, and they'll go with basically anything you want to make.
I like the angus patties from Costco as well as they're super easy to prepare, but lean ground beef is also a good pick if you don't have the steak budget.
Also be on the lookout for cheap meats that you can grill / put in the oven and snatch them up when you can.
I'm not a super good cook but most of the time I have some pasta, rice, or a salad with some meat of some sort. Bread, eggs, fruit, and veg all get in the mix from time to time based on the time of day and if I want to mix it up.
With a few different types of each rice, pasta, and meat you've got a lot to work with.
Treat yourself sometimes, get some nice ingredients and make something new that you've been looking forward to. For me I usually make lobster rolls.
As for learning to cook, America's Test Kitchen. Find recipes you like, then see what ingredients they most have in common. That's your shopping list.
Worst case, remember if you have a rough day or mess up cooking, there's always fast food.
If you get a smoker / bbq / slow cooker you can bulk cook meat that you can freeze and eat for a week from a good day of cooking. Pulled pork can be used in a variety of meals!