I've purchased and claimed the Legacy of the Void Beta, such that my account details show it against my account:
Clicking on that icon takes me to this page with information about the Beta, however there's nothing to indicate a 'Download the Beta now' or instructions on how to play:
The Battle.Net app also doesn't have any indication of how to launch the 'Beta' mode, so I assumed it was accessible after launching Starcraft:
And yet there's nothing after launching the game that screams "Access the Beta content by clicking here right now!" either (unfortunately screenshots of the game menu seem to fail so I can't show this).
Of course, my Google-fu is failing me: everything I find simply tells me to pre-purchase the game, or how to pre-purchase the game, without any indication of how to actually launch and play it.
So, How do I actually launch and play the Beta and/or the Prequel missions?