New owner with Flashing Triangle problem

Hello All,

I am new to Benzworld so please excuse my ignorance. I just purchase my 1st Benz. A 1999 E320 Sedan. It needs some TLC as it still has the spare on the ground. I have no manual and while driving it home a flashing triangle alert appeared in the instrument panel when I got up to 20mph. I stopped serveral times and pressed buttons on the console that I had no idea what I was pushing. Finally the flashing alert disappeared and I was able to go over 20 mph, until I stopped at the tire shop for 15 min. When I left the parking lot and got up to 20 mph and the same flashing triangle alert appeared again. What am i doing wrong? HELP!