How to Mask a Photograph in Photoshop into a rounded rectangle

1. Open Photograph in Photoshop
2. Create a new layer and create a rounded rectangle with the shape tool
3. Select the pixels of the rectangle by Ctrl+the thumbnail in the layers box
4. Select the photograph layer you want to mask
5. Click the "quick mask" button at the bottom of the layers box
6. Hide or delete the shape layer