You will only need to enter one W-2 in TurboTax.
Companies will sometimes send out multiple copies of the W-2 if you worked in multiple states during the year. You will just need to enter one W-2 into TurboTax, and then add additional rows for the state section (boxes 15 - 20) to enter all of the information from your other two forms.
If the information in boxes 15 - 20 is the same for all three W-2s, you can usually disregard the additional copies.