https://ifnowcode.github.io/gammon
Currently you need to click off using the middle bar (bottom for light, top for dark) to deselect if you select and don't move. Still working out how that should behave better.
There is an opponent AI (dark player) you just need to roll the dice to initiate it's turn.
If you don't know how to play there are plenty of resources online, just search for 'How to play Backgammon beginner' sans quotes.