/3/ - 3DCG

I'm new to blender and modelling in general, how does this work? Will blender automatically create extra triangles once I export the model or will I end up with an impossible model?
In the first picture I have a triangle attacked to that face on its left, and then try to stretch it.
If I change the perspective like on the right picture I see blender is adding edges to make the stretch possible, but those edges aren't real and I can't select them.

Am I supposed to only use triangles in cases like these?