From DT Online
Blades are normally clamped in place such that the saw cuts on the downstroke, pulling the workpiece against the table.
Safety Point! All machinery can be hazardous and fingers can come into contact with the blade - these oscillate so tend to vibrate soft materials rather than cut them however. Eye protection should be worn and care taken to avoid inhaling any dust.
Note: To cut internal shapes, small holes are first drilled in the material through which to thread the blade