The stuff I got in the picture was from home depot but I think I have gotten stuff from auto zone begot that was a rust reformer primer. And yes you always want to primer metal and fillers (bondo, glass, etc)before paint. That is unless your using paint that can be applied straight to bare metal or your painting over existing paint. In the case of painting over existing paint just sand the paint that's there and spray over it. Not saying that's the right way but I have done it that way and not had bad results. And before you paint its better to wash it down, auto shops use soap and water with some chemical but I usually use a few rags and paint thinner and wipe everything down. That way I can clean everything up and give it a once over begot painting.
Fat fingered from the phone- Corey