You can see a complete list of user-definable hotkeys (keyboard shortcuts) in the Lexicon settings.
Other than those, there are a few standard hotkeys:
Esc: Closes popups and cancels actions
Enter: Plays the selected track in the track browser
Tab: Go through editable fields in the track browser or switch to Recipes in the Edit dialog
Up/Down Arrow: Move through tracks in the track browser
Page Up/Down: Move through tracks in the track browser per page
Home: Go to the first track in the track browser
End: Go to the last track in the track browser
Del or Cmd+Backspace: Delete a track from the current playlist or Lexicon. Hold Ctrl to show the popup with more options, like deleting the file from your computer.
Videos
Check out our YouTube for videos about Lexicon.