Hi aallvor,
To set the loop range you can right-click in the top timeline ruler and use the ‘set loop start here’ and ‘set loop end here’ menu commands. The timeline ruler shows a green bar which indicates the loop range. You can also use the mouse to drag this bar or the start/end handles. If the loop bar is obscured by the punch in/out bar, then you can activate the ‘L’ timeline ruler edit mode.
To activate looping, you should select the loop button in the bottom transport toolbar. The key shortcut for this button is L. When looping is activated the color of the loop bar and the timeline range is highlighted.