Here's a breakdown:

* Active Site: This is a specific three-dimensional region on the enzyme's surface. It's like a lock that only fits a specific key (the substrate).

* Substrate: This is the molecule that the enzyme acts upon.

* Binding: When the substrate binds to the active site, it forms an enzyme-substrate complex. This binding is typically temporary and facilitates the chemical reaction catalyzed by the enzyme.

Think of it like this: the enzyme is a tailor, the active site is the sewing machine, and the substrate is the fabric. The tailor uses the sewing machine to stitch the fabric together.