Although for most cuts, the primary aim is to keep the jigsaw blade straight, making a bevelled cut involves intentionally setting the blade at an angle.
This is useful when you want to join two pieces of material together at 45 degrees to form a mitre joint. Bevelled cuts also enable you to create a decorative finish along the edge of your workpiece.
Before making a bevelled cut, you will need to pivot the shoe of your jigsaw and set it at the angle at which you want to make your cut.
For more information see: How to adjust the shoe of a jigsaw?