Loops the selection in the current pattern. If there is no selection - places loop markers in the pattern (including other patterns), hold down (virtual repeat) to remove markers. If the track automation pane is visible with a selection with existing points then loops that selection.
Tools have descriptions in Main menu>Tools>Tool browser, you may find this useful.
I put all instructions there.
Loops the selection in the current pattern. If there is no selection - places loop markers in the pattern (including other patterns), hold down (virtual repeat) to remove markers. If the track automation pane is visible and a parameter is selected and it has at least one point, loops the selection in the automation editor. keybind is pattern_loop_pone
Go to Preferences>keys and search for pattern_loop_pone