In plain English, that means that GET is used for viewing something, without changing it, while POST is used for changing something. For example, a search page should use GET, while a form that changes your password should use POST.

When should POST be used?

A POST would be used for any operation which is neither safe or idempotent . Typically a POST would be used to create a new resource for example creating a NEW SO question (though in some designs a PUT would be used for this also). If you run the POST twice you would end up creating TWO new questions.

Should I use put or POST?

Use PUT when we want to modify a singular resource that is already a part of resources collection. PUT replaces the resource in its entirety. ... Use POST when you want to add a child resource under resources collection. Though PUT is idempotent, we should not cache its response.