This is a super useful funtionnality that has been integrated in Inkscape recently but it exists in other vector softwares.
Basically is allows you to do a bunch if shapes & lines, put them one on top of each others, and use them as cutting guides.
It’s a very powerful and useful vector tool, allowing you to make complex shapes quickly from basic ones. Demonstration below:
Bunch of circle & squares:
All selected and shape builder tool activated:
Click to choose what shapes to keep, hold click to merge different ones:
Results: