Do you want to create a round circle or elliptical selection in a photo? Do you want to erase or fill the area outside the selection with white, black or another color? I have PSE11, so I hope the Tools and Palettes look similar to PSE10. If so, here goes.
1. Select the Marquee Tool in the Tool Palette. By default it is set to the Rectangular Marquee. The Lasso tool will not give you a perfect ellipse or circle.
2. Select the Elliptical Marquee option in the Marquee Tools options. Hold down the mouse, click in the photo on the upper left, sweep across the photo to the lower right, release mouse. You should have a selection (AKA "Marching Ants"). You can reposition the selection by moving the mouse inside the selection, hold down the mouse and move as desired. If you click outside the mouse, you will start a new selection. If you want a perfectly circular selection instead of elliptical, hold down the shift key first and drag across the photo. The slider in the Tool Option area lets you decide how hard or soft the edges of the selection will be. A setting of 0 (zero) is a hard edge. As the numbers go higher, the edge of the selection gets softer. Move this slider before beginning the selection process.
3. To delete the pixels outside the selection, go the top menu to Select, click and hold and slide down to Inverse. All the pixels outside the selection now editable and not the pixels inside the selection.
4. If you hit Delete, the pixels will be deleted and now the background color will show. In this case it's white. To shut off the Selection, go to Select > Deselect.
