It can parse Text (HTML is allowed) for substitutions. It can also output CSS, JS, and jQuery as well as load some of CBs APIs (would depend on your needs). The inputs for each are pretty self explanatory with descriptions of their purpose and examples in the descriptions. The substitutions are always based off the viewing user. So if they're not logged in it's ideal to hide the module (set access to Registered). Please see the below for substitution usage information.
www.joomlapolis.com/support/tutorials/107-use-cases/18353-using-substitutions-throughout-cb
As for what you're wanting the module can't do that. It can show a users username, but it can't show a random users username. For that you should use the CB Online module.