If I have a W2 and a W2C for the same year, do I enter both?

If they are for the same year and the same company, then you will most likely be entering a combination of the two forms.  

Take a close look at the W-2C to determine what boxes have been corrected and be sure to use the corrected version when entering those boxes.  Anything that was not corrected on the W-2C should be entered from the original W-2.  

When everything is entered, you will only have one W-2 in your tax return (unless you have others from other jobs or companies).  Be sure after entering the W-2 that you check the box on the follow-up screen that says the W-2 has been corrected.