Both extensions (via WalkingCat on Twitter) allow users, obviously, to block ads on websites. Microsoft has promised they would be available for Edge and now Insiders can try them out. Keep in mind these downloads will work just for the most recent Insider versions of Windows 10 that enabled extension support for Edge. This feature won't be available for every Windows 10 PC user until the big Anniversary Update is released later this summer.
Also, keep in mind that even though they have similar names, AdBlock and Adblock Plus are made by two separate companies.