The ICBM API is probably for other mod developers who want to use ICBM stuff as part of there mod. The end player will never need it to run ICBM in their instances. All you need to do is download ICBM contraption, explosion and sentry. Do not open any folders. Just drag and drop them into the mod folder and you should be fine. Don't unzip anything either, Minecraft forge will handle everything for you. Before you do all that though consider using NEI to generate an item and block ID dump. (Open up the NEI menu and it should be pretty easy to work out how to do it, make sure nothing is hidden though). The id dump will make life easier for you if you run into any id conflicts. When you make it NEI should tell you where it saved it (hint: it will be in your minecraft directory too). It is a normal text file.