The screws will be facing forward or backward depending on the microscope. On most microscopes there will also be a knob or screw that locks the condenser into the condenser carrier. This allows you to remove the condenser and clean it or replace it with another with out having to completely recenter it, at least you will be in the ball park. Different condensers are required for different techniques. If you want to do phase you will need a phase condenser, the same for Nomarski or dark field.
Some condenser can do a wide range of techniques.
These are called universal condensers for the wide range of things that they are capable of. Located on the condenser is the condenser diaphragm control. This may be a lever or a dial either way this controls the contrast of the microscope image. It also controls part of the resolution of the microscope. What it doesn't control is the intensity of the microscope, that is controlled by the electronics.