Choose Tools => Distance to measure the distance between two objects. To indicate the initial point, double-click on any place of the map. Then sequentially add new points. At any moment, you can move the map or zoom it using any of ways described above.
Near each point, the distance from the previous point is indicated. The total sum of all segments is known from the popup window in the corner. To know the sum, the mouse pointer must be placed over the last point of the polyline. Unlike other points that are red, it is white with blue border. If the cursor points some other place, the total sum will also include the distance to the current cursor position. At the same time, in brackets two numbers are given: the sum of all segments drawn + the distance to the cursor (if the cursor is over the last drawn point, this distance is 0m).
When the line is on the map, move the cursor along the line to get the distance from the starting point to the current cursor position. Cursor position is marked by a white point (if put the cursor over, it becomes plus-shaped), and a black font is used to display distance value.
To clean the map and start new measurements, use the 'Reset' button.