By Furniture Mod, you refer to Bibliocraft? Or another mod? Either way, most mods tend to provide clear crisp Instructions on how to install them (including any additional Mods/cores it needs to run).
In the case of bibliocraft (which can be downloaded here http://www.bibliocraftmod.com/?page_id=48
) you'll need to first install Minecraft Forge (http://files.minecraftforge.net/
After installing Forge and running the game, a mods folder will appear in your Minecraft Directory. All you need to do then is move the Bibliocraft folder you downloaded and move it there.
Hope this helps~