How to create faces on an object

First, excuse the amateur talk-- I'm no expert to 3D design. However, let me explain what I am trying to accomplish...

Let's say I create a cube. Six sides, right? I want to paint one side one color, two sides another color, etc. I want to export it as a .DAE file and into a virtual world so that when I paint a side, it will change, and only change the sides that matched. So in my example, the cube had two sides that I want the same color, right? When I color one of those two sides, the other side would automatically change to the same color.

How can I do this? I've searched high and low, and watched countless YouTube tutorials-- can't figure it out. 

I'm currently a free user, but as soon as someone can teach me, I'll subscribe. Thanks in advance for your help!