As has been said before, don't worry about special brushes. In fact, I wouldn't even worry about 'shading' or 'rendering' -- For starters, focus on blocking out shapes. Try painting some simple still life set ups with high contrast lighting. Use fewer, bigger brush strokes to try and block out the form, rather than putting in lots of little lines and trying to get all the detail. Also if you want to get good at this, you have to practice EVERY DAY!
Check out my little doodle below and see if that helps get you started (this was done with just a normal default brush with pressure opacity)