I could not file online so I've printed out my return to file by mail. Adding a couple signatures is all I need to do, right? Do I need to do anything else besides sign?

When you mail a tax return, you need to attach any documents showing tax withheld, such as your W-2’s or any 1099’s.  Use a mailing service that will track it, such as UPS or certified mail so you will know the IRS received the return.