web method in asp.net

Question

hi guys i ma working some existing project where some feature is used but i am not getting

 

 

[WebMethod]

public static string InsertData(string username, string subj, string desc)

{

string msg = string.Empty;

try

{

}

 

please can some one explain me

 

1 .why given web method on the head off "insert data" method name

 2. what is use of this  ,what is web method

3.is it only for static method