Since you've shown an interest, I recommend you read up a little on complete
proteins. This can be found in any nutrition book (try a library, school,
on-line at webmd.com). Basically, proteins are made of amino acids. Of the
approximately twenty different amino acids, there are some the human body
needs that it can note make itself. They are needed in certain proportions
and when combined properly, make what's known as a complete protein. All
animal source proteins are complete. But if you don't consume animal-source
foods (which includes daily and eggs), your protein source may not be
"complete".
All foods have proteins, even though fruits are generally lower than most
vegetables and grains. When processed, as in corn to make corn oil, the
proteins and carbohydrates are separated from the oil so the oil that's left
doesn't have protein. Some non-animal foods are higher in some amino acids
but lower in others. Soy beans and their derivatives come closest to
complete proteins so that's why many meat substitutes are mad from soy
sources. If you eat grains and beans in the same meal or even in the same
day, for example, the amino acids combine close to what the body needs as a
complete protein.
If you eat dairy and eggs, I recommend you not concern yourself with
evaluating your protein source as long as you get enough calories for all
your energy needs. But if you are Vegan, or strict vegetarian with no
animal food sources, you should plan you meals around different foods where
the amino acids can be proportionally consumed.
Good luck. Tom