New Compressor questions

Hi..I picked up this compressor from Craigs list and have never owned one before. So here are my questions.
1. on the picture with the two gauges and a black knob in the middle..what does the knob control?

2. What is the red canister for. Now it is empty. Is there some type of filter that should be in it?

3. In the picture with the big guage and red canister, there is some sort of control valve below the guage. What is the proper settings for this gauge??

4. My HF DA sander instructions say that some oil should be used....where do I put it??

Thanks for your help