What version of photoshop?

You probably need to use the Path Selection Tool and change the path operations to Combine or Exclude in the tool options bar.

Then make the selection from the path.

Use the Path Selection Tool, click on the path outline and set the option in the tool options bar to Add To Shape Area

Could post a screenshot of your photoshop window and explain what you want to happen?

Do you have more than one path?

How did you create the Path? There are four icon the controll how path are joined. This screen capture show I user 24 elliptcial path each in Add mode. You can see this in the path Palette, Howt the layer was fille and see the Add to path ICON is active.

Crops are always rectangles its sounds more like you want to mask out the background.

You can make selection for different areas using different tools like the pen  tool to sharp well defined areas then turn the path into a selection and save selections as alpha channels. When you have all the selection you need you can combine the selection.  However for Hair its useally best to strart with a copy on one of the color channels and use Photoshop's tools on it to create a mask.

You need good contrast between the subject and the background and it helps it the original background is white or light gray.

http://mouseprints.net/old/dpr/ReplaceBG.html

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Activate the Path Selection Tool.

Option-click on the compound Path's thumbnail in the Paths panel. That will select all components of the Path.

In the options bar, click the Subtract button to ensure all components are negative.

Click on the canvas outside of the entire path to deselect all of the path. Click on the line of the main outline path to select only it.

In the options bar, click the Add button to make the main outline positive.

The compound path should be correct now.

You can target the Path and the image layer then Add Vector Mask to the image layer, or Command-click the Path's thumbnail to get a marquee then Add Layer Mask to the image layer.

You're welcome! I'm glad to have helped.