The HTTP GET method is used to retrieve (or read) a resource. In the success (or non-error) path, GET returns a representation in XML or JSON and typically an HTTP response code of 200 (OK). In an error case, it most often returns a 404 (NOT FOUND) or 400 (BAD REQUEST).
PUT is used for update capabilities, by doing a PUT to a known resource URI with the request body containing the updated representation of the original data/resource. On a successful update usually an HTTP response of 200 (or 204 if not returning any content in the body) is the return.
The POST method is usually used for creation of new resources. On successful creation typically returns an HTTP status 201, or returning a location header with a link to the newly-created resource with a 201 HTTP status.
DELETE is used to delete a resource identified by a URI.
On successful deletion usually returns an HTTP status 200 (OK) along with a response body or returns an HTTP status 204 (NO CONTENT) with no response body.