I usually make a copy of the background layer. Its not essential but can be useful if you make an uncorrectible mistake.You can do this a number of ways, I usually drag the layer onto the New Layer icon at the bottom of the palette. Name this new layer Phone Body and hide the original.Next, make sure you're working on the newly created layer, select the Custom Shape ToolChoose any shape from the top toolbar (we'll use a heart for this tutorial).Draw the shape out of the menu. its best to find a plain white part of the image so you can see the shape properly.Dont worry about the size for the moment, well deal with that next.