Answer:
To Mod Minecraft, first you have to download the Mod you want (Duh) by searching a trusted Minecraft website, such as minecraftforum.net, a very useful site for Modding newbies. When you find a Mod you want, the file you download or the page you downloaded it from (or both) will contain all the information you need to successfully install the Mods. Most Mods have the following instructions:
1) Start > Run > %appdata%\.minecraft
2) Open bin folder.
3) Open minecraft.jar with Winrar, 7zip etc.
4) Drag Mod files into minecraft.jar file.
5) Delete META.INF file.
6) Close and play!