There are also calculators listed in the FAQs that will help you determine what you need to eat to maintain your bodyweight, lose fat, gain muscle, etc, over a user-selected window of time.
First thing I realized - that the difference between tracking your "macros" and not is like programming with Word or with vi/emacs/slickedit/etc - the difference is AMAZING.
The next thing I realized - is that to get enough protein if you're even moderately active, you have to eat A LOT - eggs, milk, meat, tuna, and even then I still have to supplement with protein supplements.
Now, combine the diet knowledge with a beginner weight training program like Starting Strength and the effect is amazing. I've gained 10 pounds of muscle and lost 10 lbs of fat. I've doubled all my lift numbers (which are still admittedly quite low) in four months. I have far more energy and other activities - I occasionally play tennis - I play better and feel stronger.
Edited to add - and most importantly, use something like myfitnesspal.com - which is free, has a great app, and has millions of food items, and track everything for just a few weeks. it will teach you what protein/fat/carbs common foods you eat have.