Protein is essential to life, we all need protein to build our bodies. We can get protein from milk, meat, fish, eggs and plant products. Most westerners eat as much protein as they need but protein may matter for vegetarians especially vegans, for anyone who for animal welfare reasons or health reasons is serious about limiting meat and for poor people. We can get all the protein we need from plant products. Vegetarians need to make extra effort to make sure they get all the building blocks we need to make human protein. Getting the proper balance of protein is easier for vegetarians who drink milk and eat milk products than for vegans but vegans can be healthy. 
There are nine essential building blocks of human protein, which we must get from food. (Scientists call these building blocks amino acids) Meat contains all the essential amino acids humans need; most plants do not have them all or have some in the wrong proportions for human protein. However eating a mixture of plants, such as both wheat and peanut butter, or rice and beans, provides all the essential amino acids needed. Soy products like tofu provide all the essential amino acids as does Quinoa but are not the only way to get the protein you need.  Barley and Rye can also complement the protein from pulses.