It’s just different ways for HTTP requests to be made and generally infer that other stuff will happen when you perform a given request
Loosely:
GET will only send “arguments” in the “URL”
POST will do either.
GET’s are repeatable
POST’s generally are not (as different data would be POSTed each time)
POST’s also allow more/other kinds of data to be send other than the limitations of the query string that only GET allows
More reading: