Markers and flags
Markers and flags are great to point users to specific areas or elements on your screenshot. Both objects are available via the flag icon on the screen editor menubar (the one that says "markers" when you move your mouse pointer over it).
You may change the size of your marker to make it fit around an icon, a box or any other element (it may be square or rectangular). Note that the marker border is always transparent so you can still see what's hidden underneath.
Flags and markers can be moved on your screen by dragging them with your mouse pointer.
Don't forget to press the green save button to save your changes!