If I already filed one of my w-2's before I found out I have a 2nd one what do I do? There's an option to add another w2 but I already e-filed the first one.

First you will need to wait and see if your return is Accepted or Rejected by the IRS. If the return is Rejected you can go back in and fix the mistake without amending. If the return is Accepted you will need to WAIT until you receive your refund and then Amend.

Follow these steps to amend:https://ttlc.intuit.com/replies/3288565

After i amend what will happen? I need the money for a car so I was wondering if I could just save the second w2 and file it next year. My redund was already accepted. Will they take money back after I amend it

They take about 16 weeks to process your amend return which has to be mailed in. If you owe something after you amend you would subtract it from your refund amount. Do not amend until you receive your refund.

If I owed money would I send money back?

Yes you would deduct what you owed from the refund you receive once you file the amendment. <a rel="nofollow" target="_blank" href="https://ttlc.intuit.com/questions/2817197-i-received-a-refund-when-i-filed-but-now-i-owe-taxes-on-the-amendment-how-do-i-handle-this">https://ttlc.intuit.com/questions/2817197-i-received-a-refund-when-i-filed-but-now-i-owe-taxes-on-the-amendment-how-do-i-handle-this</a>

And you cannot save the W-2 and file it next year.  A 2017 W-2 must be filed with your 2017 tax return.