Don't think that's a stupid question. It's not exactly intuitive until you think about it.

What is the least amount of points to make a flat polygon (face)?

1? No that would just be a point.
2? No that would be a line.
3? Yup! You can definitely make a single flat surface no matter what as long as the three point vectors are linearly independent.
4? Nope. You can technically have non-faces with 4 points.

Let's take a look:

From the top, both these polygons look flat (left is a quad, right is a tri):
http://i.imgur.com/BSCQ9PB.png

However, you'll notice that from a different angle, the 4-faced polygon isn't actually flat...
http://i.imgur.com/lCLn9w2.png

3D Programs can work with quads just fine, but engines limit their models to tris because that is the minimum amount to make faces. When you export your own models via the smd exporter, you'll notice that it automatically triangulates your model (Try it: Export a test model as an smd file > import it back into blender > suddenly it will be made up of tris instead of quads).

Obviously modelers don't model with tris... They model with quads first, and then go in and detail (manually editing stuff, sculpting, etc).

Thank you very much! This was helpful. Also, your modeling guides are very helpfull!

"Obviously modelers don't model with tris..."
...
...
...
why did i ctrl + T and then save?!??!? T-T
xD

Fear not citizen!... use Alt + J so convert a selection of triangles into quads!

But not with 100% accuracy. It's easy to go from quads to tris. Not so easy to go from tris to quads.

Yeah you got me. Still It's a good start and good for people to know if they don't. For the few triangles that don't convert to quads then i would recomment selecting the edges you want to get rid of and press x to delete and choose disolve edge.