There are a few different ways that you can outline a shape quickly in Photoshop. One way is to use the pen tool. With the pen tool, you can click around the edge of the shape to create a path. Once you have a path, you can then add a stroke to it.
Another way to outline a shape is to use the selection tools. With the selection tools, you can select the shape and then add a stroke to it. You can also use the eraser tool to erase part of the shape and then add a stroke to it.
If you are not careful, you can easily select the wrong layer when outlining a shape in Photoshop. Make sure you have the correct layer selected before you begin tracing your outline. Otherwise, you may end up with a messy selection!