You'll need a Creative Cloud account to purchase After Effects, from there you can pay and use it month by month or annually. A few years ago Adobe made to move from selling physical products to only selling digital subscription based products - if you're someone who will continuously upgrade from year to year when new revisions become available, this new method of purchasing will save you money. However, if you're someone who just wants one piece of Adobe software and doesn't intend to upgrade year after year, if can be a little off putting.