Minecraft Help: how do I enable a mod?

I downloaded it, I put it in the mods folder, and I can't see how to enable it. I did it before but I can't remember how I did it.
http://www.minecraftmods.com/mine-painter/

Guest 27.01.2016

Here is some instructions for mod installation.
1. Make sure you have forge installed. (Make sure the mod is one that works with forge, and make sure you have the mod and forge for the some version)
2. Download forge and install it (Open the forge app after you download it)
3. After forge installed there will be a new version in the minecraft launcher (In the area where you can select different versions of minecraft, it will be on the bottom)
4. Put the mod into the "mods" folder, open up minecraft and make sure your running the forge version of minecraft

Garrett 27.01.2016