96 ultima with voltage problem

I know nothing about this car so I have to ask. It seems that there is a voltage problem. Recently, the air conditioner quit and when I turn it on the radio goes off for a second or two. The air fan blows slightly. The battery light is on and the brake warning light is on for some reason. Does this car have a voltage regulator and if so where is it? Or would a low battery cause this. The car starts fine. It seems that things like the power windows work but they are very slow now. Anyone have any answers that can help? Thanks