When you need to cut a shape inside a piece of wood, a plunge cut is pretty much your only choice. Typically, you might use a drill with a small bit to bore a hole that you can drop your jigsaw ...

When you need to cut a shape inside a piece of wood, a plunge cut is pretty much your only choice. Typically, you might use a drill with a small bit to bore a hole that you can drop your jigsaw blade ...

You can make your own plunge cut sans a drill by leaning the front edge of the jigsaw against the wood surface and slowing pushing it down into the wood as well as pulling it across the wood.