Turning a path into a mask

Make a path around the image which is to have its background masked in the normal way.

Make sure that the path is active in the Path Palette.

In the Layers Palette, Select the layer to be masked and reduce the Opacity to about 33%.
Place a layer filled with opaque white on the layer below.
Tip: this will make the Path more visible against the image which will temporarily be much lighter.

Check the Path to see how it fits around the subject.

Enlarge the image to 200 or 300%, and again check the edges.
Tip: Ideally, the Path should be about 2 or 3 pixels in from the edge..

With the path active, select the icon Load path as selection.

The path is now loaded as selection.

Invert the selection, so that the subject will be white on the mask and the background will be black.

1. Ensure that the Subject layer is visible and selected.
2. Ensure that the new background layer is also visible.
3. The white layer is not needed any longer and can be turned off or deleted.
4. Now Select the New Layer Mask icon.

This should make a new Layer Mask, showing the subject against its new background.

Enlarge the image to at leat 100%.
Use the Refine Mask Palette tools to complete the masking.

Check the final image and if necessary return to the previous step the further refining the masking.
Note: the original path is saved with the image.