Recently my Camaro has been starting up and it idles high but then idles low and high and then just stalls, So in order to keep the vehicle running I have to tap the gas . I just took it to a mechanic and he says I need an O2 Sensor ? I am new to the whole mechanics in cars and was curious what exactly the O2 Sensor does and if that will fix my Idle ?

Also he says I need a condenser which I am assuming is for my Air conditioning ? I put Freon into it and got a new AC Belt and you can hear the compressor coming on but it only blows out the top and bottom and its not very cold , So him saying I need a condenser is right ?

Also when I turn my brights on at night they work perfect but If I leave them on to long they go out completely and I have to switch back to my regular lights for a few minutes then go back to my brights and I have to keep repeating this process . Any Clue ?

O2 sensor is located on the driver side exhaust manifold. It sends signals to the computer to add more/less fuel. This could make your car stall if the O2 is faulty and sending the wrong info to the ECM. A new one may or may not fix your idle. I suggest a tune up is in order if you recently just purchased the car or have not had one in a lng time.
If your low on $$ I would not be to worried about a condenser unless it is very hot where you live.