I’m not very good at using the Shape Builder tool because I’m somewhat confused at seeing how it works. But the thing I’ve learned about is that certain lines and shapes of the object can disappear when you drag different lines of the shape. It’s very handy to get rid of undesired parts of an object or shape. Say if you want to get rid of a circle in a magnifying glass, use your shape builder tool and drag to get rid of it. It takes practice, but if it doesn’t work out property, just rely on your own knowledge and methods to change an object or create a new artwork.
Alice's Blog 