Kendyll, that is a great question and a very common question. I appreciate your decision to build something and change the world in a better way. Most of the engineering schools have common courses for all engineering majors in the first 2 years and the last years is where you decide what major you want to specialize in.
First thing is to educate yourself with the various majors within engineering. Following is one good resource I recommend going through:
If you need more information on any particular major, you can use Google or WikiPedia.
For all engineering majors, having a solid foundational knowledge of math and science is very helpful.
Once you get a basis idea about the various majors, you should be able to shortlist few of the majors you would like. Again let's say if you get into a college into Mechanical Engineering and you figure out 1 or 2 years into your college that you like some other major, you can always make a switch by meeting the pre-requisites. The switching might delay your graduation slightly, but you will graduate in a major that you can see yourself working in future happily. All the best.