1. Get Win Rar or 7 Zip.
2. Navigate to /username/appdata/roaming/.minecraft/bin/minecraft.jar and right click on it. Select Open With > WinRar.
3. Drag and drop the files/folders in the folder which the mod is in.
4. Delete the META-INF Folder inside Minecraft.jar
5. If the mod requires Mod Loader (Google Search Mod Loader and find it for the current version) and drag and drop the class files from your mod loader folder into Minecraft.jar
6. Run Minecraft and enjoy the new mod!