If you do a search on the forums for “protein,” I imagine you’ll come up with a lot of information.
In general, the body loses a certain irreducible amount of nitrogen every day. A study was done, quite some time ago, and the average nitrogen loss across all the study participants worked out to 0.6 g of protein / kg of lean body mass / day. Therefore, the daily recommended amount of protein was set at 0.8 g/kg/day. But as I recall the graph from this study, the nitrogen loss was all over the place, and 0.6 was merely the average, so some people appear to need rather less, whereas some people appear to need rather more.
The good news is that we apparently have an instinct for eating the right amount of protein. You will see many threads on this site by people who found they needed to increase the proportion of protein in their diet in order to assuage their hunger, and by others who find that more fat in proportion to their protein suits them better. The Dudes recommend getting between 1.0 and 1.5 g/kg, and some experts recommend up to 2.0 g. And remember that most meats are around 25% protein, so if you want 100 g of protein, you need 400 g (14 oz.) of meat.
In addition to the quantity of protein needed, there is also the matter of essential amino acids, which the body cannot make from other amino acids. Beef is the meat which contains the essential amino acids in the necessary proportions, though most other meats come pretty close. The “quality” of a protein is judged by how closely its amino acid profile matches the needs of the human body.