HTTP Request Action - Understanding HTTP Methods

What are the HTTP methods

Here is an excerpt from W3schools : 

Link : http://www.w3schools.com/TAGS/ref_httpmethods.asp

Method	Description
GET	Retrieves a desired object
HEAD	Same as GET but returns only HTTP headers and no document body
PUT	Uploads a representation of the specified URI
DELETE	Deletes the specified resource
OPTIONS	Returns the HTTP methods that the server supports
CONNECT	Converts the request connection to a transparent TCP/IP tunnel

How do I know which HTTP Method I should use?

Always refer to your application's API Reference. A good, comprehensive API documentation will always mention the HTTP Method that is used for each HTTP Endpoint.