When I put it on auto and heat doesn't work, if I put it on fan and heat it blows cold air only

Your furnace is broken. Could be many things, pressure switch, hot surface ignitor went bad, who knows.
Read the FAQ at top of page maybe you can get some hints and post back

Look into the small round glass on the bottom door of the furnace. The flashing light will give you the code telling you what's wrong. 3 quick with a pause 4 fast = code 34 ignition failure. The code should be on back of the furnace door.