An envelope in Ability is simply a normal document with a paper size set to envelope. To print envelopes, your printer, and the software that comes with the printer, must support the envelope paper size.
The usual scenario is that you’ve type a letter with an address in the top left corner and now you want to print the address on the envelope:
Select Envelope from the Tools menu
Choose the envelope paper size to match your stationary and select OK.
Ability will copy the address block, create a new document and paste in the address. You can now print or return to the original document using the Window menu.
As a refinement, you can determine exactly what text gets copied to your envelope by first selecting it and then following steps 1 and 2 above.