Online tax preparation and e-filing for 2018 have been closed permanently now. You now need to download desktop software to a full PC or Mac (not a mobile device) to complete your 2018 return, and it will have to be printed, signed and mailed. You cannot e-file.
If you already paid for your online software you can ask customer support for a download of the desktop software.
If you have not yet started 2018:
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.
If you have specific questions about how to enter data into your return, post your questions here.
You are welcome.