It's really simple.
To find your state's Election Board Web site, just do a Google search.
In the menu you will find information regarding absentee voting. The form you print, fill out and mail to the address indicated is this ==> Absentee Voting Application. Each state's application looks different.
Everyone who is full-timing needs to do this NOW to insure that you will receive your ballot in time to vote and mail your ballot back to your Election Board BEFORE the election. Each state has a different absentee ballot deadline. Your application should give you those deadline dates and times.
If you have not registered to vote, it's not too late to do that also, but time is running out quickly. Registering to vote can also be done by printing the application from online and mailing it to the address indicated.