You can measure distances using the Ruler tool



Click on then click on the starting point on the map.


You can add as many points as you like by clicking on the map.


To end the ruler click again on the last point and the point icon will turn red


You can move a point by double clicking on it


You can edit the point by right clicking on it


The line you created is added to the GPS dialog



You have the same functionality as a GPS track (for example view elevation, display distance, save as a GPX, etc.) See Managing GPS files for more help