It depends on what language you're using and what library (if you're using a library) you're using. With LFS_External I'd use
InSim.Send_BTN_CreateButton("Button Text", "Title", Flags.ButtonStyles.ISB_DARK | Flags.ButtonStyles.ISB_CLICK, 5, 30, 100, 10, 96, 1, UCID, 40, false);
.
Nobody can help you if you're going to be terribly ambiguous, and ask the same question, where there's many many many times more information.
Honestly, you need a lot more skill than you seem to have. If you're asking where it needs to be thrown, then I think you should learn C# or whichever language before you attempt a project. Trying to wing it like this will only make people annoyed with you and unwilling to help.