Open the drawing panel to toggle the drawing mode, in this mode: you can draw shapes that will be visible to all players. You can also enable player drawing if you wish.
Click on the Ruler tool or hold R to toggle the Ruler, you can then click-and-drag your cursor onto the board to calculate distances.
The distance per grid cell and units can be set in the Grid's parameters.
Pings are useful to bring attention to a specific part of the Board and communicate easily. Hold the P key and click on the Board to ping an area.