To get the current user, you can run:
To store the data in a variable, you can use:
Finally, to make this available as a reference, there's a hoop that you have to jump through where some logic editor action needs to set the variable (with the Set Variable) action for it to become recognizable to use as a reference. You can hack around this by e.g. creating an always-true if action on the page load event (deselect components and click the "Add Logic" button to access the logic editor for the page load event), and then adding the Set Variable action to the false branch (which never fires).
Then, you'd mirror the custom queries video tutorial, but just use the storage variable. Note that you'll probably need to URI escape the username to use in the query.