Notes:
To give quick access to important commands I created the toolbox. Most of the commands concern the creation of selections.
Use the R button to restore a selection or to transfer it to an other image.
A command I added is the to delete the last segment of a polygon selection. Allowing to correct errors without re-selecting everything
When you make an area selection the area will be closed automatically.
You can create complicated selections by subtracting from and adding to an existing selection.
The selection in the example contains the areas around the two nuclei.