Click on the selection tools (Dotted Square or Oval. Both are located on the Top left of the tool selection) and then click on a particular area to select it and then stretch the box out to where ever you want.
Square Selection Tool: Rectangle
Oval Selection Tool: Ellipse
Then on the brush menu, all the way at the top, the Clipboard brush should be available and be using the image you selected.
To make a border - There are several ways you can do this.
1. Take a small brush, preferably a hard and smooth circle brush and brush around the edges to make your border manually by hand using the shift and click method to make straight lines.
2. Select the Image (CTRL+A) and then select EDIT at the menu bar and click STROKE SELECTION. Then just follow this. The Line Width depends on how big you want your border to be.