This guide will explain how to install mods that have been made for the Minecraft Forge API.
1. Make sure you have already installed Minecraft Forge.
2. Download a mod for Minecraft Forge from this site, the Minecraft Forums or anywhere else!
3. Locate the minecraft application folder.
4. Place the mod you have just downloaded (.jar or .zip file) into the Mods folder.
5. When you launch Minecraft and click the mods button you should now see the mod is installed.