proteins are an essential part of your diet – if you don’t get proteins, sooner or later, you’ll drop dead. This is because the body cannot manufacture all the amino acids to build its own proteins. These “essential amino acids” need to be taken up in your diet.
That doesn’t mean you need some fancy protein supplements, though. Just what’s in your normal diet. Proteins are in meat, milk, in beans, … the list goes on.
As the others have said, proteins are essential for your diet. For example, when I culture human cells we include the amino acids from proteins in the media that is used to grow them in. Without these, the cells would not survive.