We didn’t want to announce Wikifunctions before you can edit it (what’s a wiki if you can’t edit it?).
It is currently in locked-down testing. We have been slowly configuring and testing the wiki, the first new multilingual project in over 12 years! It is more complicated than a normal new wiki, in many ways.
We are expecting to open it to broader editing in the next few days - on or after August 1. We are planning an announcement at that time.
The intended built-ins are listed at https://meta.wikimedia.org/wiki/Abstract_Wikipedia/Reserved_...
There are more interesting examples of some user-made functions at the Older Beta-deployment location the team has been using for the past year: https://wikifunctions.beta.wmflabs.org/wiki/Wikifunctions:Ma...