Think of a protocol like a language; if you just blurt out sounds no one will understands, but if you make sounds that correspond to an already agreed upon meaning, it becomes communications.

The same thing is true for sending 1s and 0s; they are meaningless unless the other end understands them and a protocol is “the agreement” both ends use to communicate.

damn, people here are too kind. literally explaining everything op asks when it can literally be searched on wikipedia lmao…