Car shuts off while driving

I just got this car I knew when buying it I have to fix it up a bit. The problems I know it to have is a bad muffler/exhaust that is always easy to fix, battery, brakes. I am sure it can use a tune up. Now I do not know if any of those things can cause the car to shut off. I am going to go into details of what happen. I got the car around 3:00 yesterday when I got it the car started right up and went into gear and drove other than the muffler/exhaust it was running fine. I had trouble getting the hood up but when I did I had to put oil in it but all other fluids was good. I continued to drive around for a few hours. I was on my way home around 1:30 am when I got off my exit home I realized my heads lights were not on but was before the would not turn back on but the high beams did for a minute then they turned off. After that the car had shut off, but I started again then shut of again. It would start with no problem every-time it shut off but my lights did not come back on. I made it home and left. I went out this morning to see if it will crank it did but my horn is beeping and will not stop. The horn sounds as soon as I turn the key but the horn did not work yesterday. What can be causing the car to do this is it electrical or a sensor? How can I get the horn to shut off? I do not want to drive while horn is blowing.