C# attributes and how it works

Please explain me why we should use attributes.. (other then declaraing obsolete)

say for example

[WebMethod()]
public void Test()
{
  //some logic
   ...  
}

In the above code, I am using WebMethod() as attribute. I may have some properties like Description, Enable session etc., But my question how it is bounded with the particular class member (in our example Test()). Can I create object of attribute class? Is it like Inheritence?

Please explain

Regards,
T.N.Nagasundar