How do you "tag" another forum member in a post?

The Discourse developers themselves thought that a forum user guide was unnecessary, and that the best way to learn to use Discourse forums was via trial and error.

Everyone who creates a Discourse forum account receives a PM with a list of Tips etc …

The “adminbase” (people who use Discourse to run there own forum sites,) kept asking for a User Guide, so one of them started a community project. It was announced over on the Discourse Meta (likely a GitHub project.)

Discourse also has a "learning bot named @discobot