Key stuck in ignition,security system (by 5 users)

almost same problem, was driving the car starting acting up, it died and now will not start, key is stuck in ignition will not turn back to home

I get home (luckily) and I try to turn off my 2000 cadillac seville sts to open up my garage with my keys when all of a sudden the key is stuck in the ignition. My caddy still turns on but the key was stuck and wouldn't come out. So I take my garage key out of the ring to open up my garage. I park it in my garage with the key still stuck. I mess with it by turning it from left to right constantly for about 7 minutes stuggling and somehow finally releases the key. I have no idea how I got it to release. When the key was released, for some reason starting the car up to see if it was fine came across my mind so I put the key back in and try to start it and it wouldn't start now. The security light was on and would not come off. I call up my mechanic and he comes down to take a look at it. At first he thought it was the key (becausen its kinda worn out and thats the only key I have), then he thought it was the ignition or some sort of electrical problem. He then noticed a tiny button underneath the steering wheel and he pressed it and held it (trying to start the car). I have no idea how he got it to start and neither did he but he was just messing with the button and he got it to start. What I want to know is how to properly do that so when it happens again I know. Thanks a bunch!

HOW DO YOU STOP THE SECURITY SYSTEM FROM DELAYINY STARTING THE CAR FOR 3 MINUTES. ALSO, THE HORN SIREN HAS BEEN GOING OFF UPON LEAVING THE CAR.WE BOUGHT IT USED, HOW DO WE STOP THIS FROM ACCURRING?

turned ignition switch to start car, lights went off and key will not come out of ignition.