The model editor and Poly surfaces

[The chaser]

Hello everyone. Well, the case is that i was going to enter in the modeling world, and my main objective was to modificate the Brute, but it doesn't seems to be so easy as i thought. First, i tried to make something less complicated (A post with a sphere, actually without an use). The main problem is that in other entities i saw Poly surfaces, but the model editor doesn't let you put a "poly surface".
What I have to do? May i use another program? The material editor, or something? I'm made a mess. I would really appreciate help.