I just changed my oil and oil filter but my 05 chevy colbalt still says 0% oil life

Oil life does not reset on it's own when you do the oil & filter service.... Go to Google and search "05 cobalt oil life reset"...

Read your owners manual

Turn the key to the run position but don't start the car. Depress the gas pedal slowly to the floor 3 times. That will reset the computer to 100%.

Do you have a "reset" button on the dash? If so, scroll until you see "oil life" and if it is at 0, push and hold the reset button until it goes to 100%. Same as resetting the trip meters, the average speed indicator, and any other information you need to reset. Like Fordnut said, consult your Manuel. If you had a garage do the change, go back to them and have them show you how to reset the meter. Or drive into a Chevrolet service garage and ask the service writer how to work the settings. I did it a lot on my new GMC until I finally found out how the new electronics work.

Or you could just do what I said in the previous post...and yes, its all in the owner's manual.