I can't get any mods in minecraft to work?

Recently, I got a new iMac and had installed minecraft on it. Just the other day, I watched a tutorial on how to put mods into my minecraft game, though they don't seem to work.
The mod I had tried was the Pixelmon mod. Yes, I installed forge, along with the most current version of pixelmon. I open my game to play minecraft (in the forge account), though when it opens it doesn't allow me to play on the pixelmon mod.
I did install forge correctly, and placed the.zip in my.minecraft folder (in the mods section) though it still doesn't work.
I tried this with the Fossils & Archeology mod as well.
I'm not quite sure if I'm doing something wrong or not, though help would be appriciated.