For starters, you need to have the document in pdf format.  If you are using a fillable form from the IRS and type in the data, you have a pdf form.  If not, then you need to scan the form.  Once you have a pdf, then click on the e-file tab and click "attach pdf".  Click "add attachment" and go to where your pdf is stored on your computer.  Select "type" and if none of the descriptions fit your cause, select other and then the last step is type a description where noted.