Here's a small tutorial for you. Have a look at it.
Remaining in the same workbench, click on "measure between" as shown in the figure.
Click on the icon shown and select the point
Select the other point between which you want to measure the dimension.
The result will be displayed as shown. Click OK.
Now if you want to measure any diameters or radii use the following command
Select the diameter you want to measure and the result will be displayed. Click OK.