Selection and Learning in Photoshop.
In Adobe Photoshop one of the most important concepts is Selection.
See in your tool area. There is a tool named Rectangular Selection Tool.
Use this tool on your image to select an area of the image. This lets Photoshop know that that's the area you want to work on.
Selection and making a square.
To add to a selection, hold Shift before dragging.
Tomake the selection exactly square, start dragging, then hold Shift.
You can press Ctrl+D to "deselect" and remove the selection at any time.
Elliptical Selections and subtracting Selections
Hold down on the Selection Tool on the Toolbar, and choose the Ellipse.
To move the selection, just click inside it and drag.
Holding Alt while selecting subtracts that area from the selection. I've done that with the Ellipse Selection Tool