How can I get key out which is stuck in ignition of 2008 cobalt. It also won't start

The steering wheel may have been turned when the key was removed. So when you try to turn on the key, turn the wheel one way and the other way to release the pressure on the key. The key should turn ok.
Hope this helps.

This can happen if the battery is low / dead. To solve, connect a set of jumper cables between the battery in the Cobalt and a running car's battery. Shut off the running car. In the Cobalt, make sure all accessories (lights, radio, fan, etc.) are off. Step on the brake, then move the gear shifter fully into the PARK position. Next, either attempt to start the engine, or turn the key to the OFF position and remove it from the ignition.

I hope this helps & good luck!