How to make this happen?

[bdcahc]

I am trying to make a game where it has a toolbar, that u can click thing on it, and place thum, then those thing would do what it needs to do. BUT how do you get a itam on the toolbar you crated make thing you drag on to the game... example, of what i am doing, if you know the games, Red alert, Command and conquer, or westwoods studio. any of those that is what i am trying to make too,