Given have two shapes for example. a star (blue) and arrow (no fill). The arrow has a green stroke.
How can I make the portion of the star which is behind the arrow transparent, but retain the green stroke on the arrow?
Hold down the Command/Ctrl key and click the layer thumbnail for the arrow in the Layers Panel. This will load the arrow shape as a selection.
Select > Inversefrom the menu to invert the selection
Highlight the Star layer in the Layers Panel
New Maskicon at the bottom of the Layers Panel
This creates a mask which hides the portion of the star underneath the arrow shape.
It is difficult to know if the mask will be entirely correct because there are a couple of ways those shapes may have been created. The above assumes they are shape or vector layers. If the arrow is not a shape/vector layer, you may need to then grab a brush and paint black on the mask you just created in the center of the arrow to hide that portion of the star.