I Want to develop an application from which user can login into the particular website which sends SMSs,
so ultimately we can send SMSs using application without opening website..

i dont know how do i code for that,

can anybode help me ??

thanks in advance

define: particular website?
are we talking about a commercial site for which you need to be registered/licensed?

You should start by checking if they have some sort of API. If so, what you're trying to do shouldn't be too hard.

So I'm supposed to use SMS that would be pay per login, which needs some to contact some application that may attempt to login if it can find login form, instead of opening browser and login directly to website where data program it this days already part of many plans without extra charge.
I think you are going in absolute wrong direction technically and business wise.