I went to the Installing Mods website on minecraft.gamepedia.com, and I'm on step 9: "Open the class files from the mod with an archiver such as WinRAR or 7-Zip and copy-paste the files into 1.6.4_Modded.jar. Do not close the archiver yet." But I have no idea what class files are or where to find them. Please help! Thanks!
Added (1). I'm installing Dr. Zhark's Mo'creatures mod.