LoFaroNYG

Hello, my name is John and I am new to this forum. I bought a 1999 Chevy cavalier Z24 last week. This was my second Cavalier. My last one was a 99 too, but had 250,000 miles on it. So, I sought out to get one with less miles and bought this current one with 102,000 miles on it. My question is this, today while driving it my Brake P ! lights came on all of a sudden. There really wasn't a difference in the brake and I personally hadn't used the E brake at all. I drove it for a week before this light came on, so I don't know if it could have been the previous owner or not or what it going on. The previous owner was an older guy and a shade tree mechanic. He replaced everything on the car. On the brakes, he informed me that they'd have to be bled and these little gold rings would have to be put onto it that he hadn't put on yet. I am not very car savvy, my brother-in-law does all my car work so I have no idea what those gold rings are. But, what I want to know is what this problem could be with the brake P ! lights coming on. This car was kept in pristine condition, I live in upstate New York and there isn't a spot of rust on the entire car. The car starts without any problems, it drives very well and is the quietest car I have ever owned. I trust the guy that I bought it from and don't believe that he would knowingly sell me something that had issues. But, I am confused of what to do. The only other issue is that the airbag light is constantly on. I have no idea why. This car just passed inspected at the end of July. I know that a new after market car radio was put into the car recently, I had heard that wiring radios up wrong could sometimes be the problem with the airbag light coming on. I don't know though. Any advice with these two issues would be really appreciated! Thanks a lot for reading!