"Mod" is short for modify or modification. You can install these mods into Minecraft and they will modify your Minecraft. All mods add something. As the mods get bigger they start to have to break off into different parts. The main mod then is no longer all you need. You'll need plugins and addons to complete mods like Flan's Modern Weaponry mod. That mod is so big that if it could all fit into one pack, it would have over 1,000 files. You download the addons and plugins separately. Most mods will have installing instructions. If not, Youtube can always tell you how to complete something. The biggest mod I know of is the Pixelmon mod. It doesn't have any plugins or addons but it has over 2,000 files. Mods can add...