Hi, Amanda
Just select the Polygonal Lasso tool. Click once where you want each corner to be. When you get back to the starting point, you'll see a little "o" by the cursor that means you're back where you started. Click then to close the selection. Create a new layer and type Option/Alt + Delete/Backspace to fill the selected area with the foreground color. Now you can clip photos or papers to that layer! Repeat on new layers for each shape. :0
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Cassie
My Gear: Nikon D300s w/18-200mm VR & 50mm 1.4
Software: Adobe Photoshop CS4, PSE 10, Lightroom 2