My quad looks like two triangles I'm a beginner and I don't know what's going on.
Some faces I've made look like two triangles glued together with different angles. 

Removing doubles didn't do anything, nor flipping normals.
All faces (quads and n-gons) will be divided into triangles when they are rendered. Depending on the engine the solution for that triangulation will differ a bit. This is a normal thing. If you don't like how they are triangulated you will need to do it your self.