This is a Sabre Saw, aka, Jig Saw. This saw uses a blade that travels up and down. This cut is being bad using a piece of wood as a straight edge. The line that needs to be cut was marked at both ends, then the wood was placed 1 1/4" from the line. This is the distance from the edge of the base place to the blade.
 This saw is often used to cut curved patterns. It is being used here to cut an opening in a flat. You can get an assortment of blades to cut a variety of materials, including: wood, metal and plastics.  1u4.jpg
 Be sure to always wear safety goggles when using one of these tools.  1u5.jpg
 You can see that the blade extends below the work you will be cutting. Be careful not to cut into the table  1u6.jpg