Thanks so much, I changed my modid to all lowercase and it worked! I have one question left regarding file structure, but that would involve posting a screenshot(I don't have internet at the moment and am writing this with my phone...), so I'll try and have that up in an hour and a half or so.
NOTE: Okay, never mind, the picture didn't want to be inserted into the thing! Anyway, how should I set up my packages and directories? Right now, inside of the main minecraft folder, I have the packages "assets.firstmod.textures.items" which contains the item textures, "net.firstmod.mod" which has my main FirstMod.class, and "net.firstmod.mod.items", which has a template class for setting up Items.