I can't remember how I set it up, but my county emails me a link to an online absentee ballot. I log in, fill it out and then I either email it (printing and re-scanning the signature page) or I can post it back.
Before we had a scanner, I took a photo of my ballot pages with my phone and emailed them as images (the instructions give the details on how to do this). It didn't look pretty, but it was clear and did the job.
I don't remember it being difficult to set up. I think there was a link on my county's webpage on how to register to vote if you're living abroad or overseas military.