#paste into

Follow these steps to fill areas of your raster artwork in PS with transformed PATTERNS:

First, copy an area of your PATTERN, using the Marquee Tool (rectangle selection big enough to fill the desired area)

Create a New Layer above your artwork that you wish to fill.

With the Selection Tools (Lasso or Magic Wand work best for this type of selection), create a selection of the area you wish to fill.

Go to Edit>Paste Special>PASTE INTO and your selection will be filled, while keeping the Pattern on a separate masked layer.

Command+T to free transform and scale/rotate adjust your pattern to align with your selection.

If you wish to WARP, choose Edit>Transform>WARP and use the vector handles to WARP your pattern into the desired shape.

To Paste INTO:

Follow these steps to insert a copied or cut selected image into a selection outline:

Make the selection on the layer that you want the image to fill. This is the destination layer.

Select the image that will fill that selection. This is the source image.

Choose Edit→Copy.

Return to the destination layer and choose Edit→Paste Special→Paste Into.

Photoshop converts the selection outline on the destination layer into a layer mask. The pasted selection is visible only inside the selection outline.

Copied from: http://www.dummies.com/how-to/content/how-to-use-the-paste-special-commands-in-photoshop.html