When I moved out, I knew how to cook several things, but didn't really appreciate the need for full meals; eating just one food group can mess you up (unless you're a vegetarian/vegan and know what you're doing; that stuff takes real effort to do it right without causing problems). I've known people that tried to just cut meat out, and live on cereal and top ramen, and started getting panic attacks, major fatigue, etc, until they started eating real food again. It's not only about gaining/losing weight or some theoretical future problem; it can screw up your ability to get through the day.

Basically, just make sure that you get all of the basic food groups on a regular basis, even if the veggies are frozen. Rice is easy to make and you can cook a few days' worth at a time. Try to get some whole-grain stuff fairly often; you'll feel better.

This doesn't seem to be the popular way to do it but, when it comes to learning to cook, I got the most from starting with the basics. Just like starting with the different cuts of chicken (breast, thigh, leg quarters, etc) with very basic seasoning teaches you how it cooks and what it should taste like, so when you do a more complex recipe you know how and why it comes out the way it does. Chicken thighs with just salt, pepper, and garlic powder is still one of my favorite things (with crispy skin), and is cheap and easy. You can find leg quarters for around a dollar per pound, if you're broke.