By default, NodeBB has nodebb-plugin-markdown, which allows users to use the common markdown format in their posts.
**this is bolded**
this is bolded
It's fully documented here: https://github.com/adam-p/markdown-here/wiki/Markdown-Cheatsheet
At this time, it is not possible to "post anonymously" when logged in. You would have to enable the "reply to topics" privilege to a specific category for guests, and then your users would need to log out to post as a guest.