Prash, numbers inside load on startup tag means :- Let suppost that you have 3 servelts and that you want to start at the starting of the server itself. You have one more req. that servlet A should start first, then Servlet B, then servlet C.
This you can do it by using load on startup tag and numeric value inside it.
For Servlet A
For Servlet B:-
For Servlet C:-
In this way you are telling to server that i want to load these servelts in above order.