everse engineering is a process of taking an existing thing and using it to create a new thing. MySQL Workbench accomplishes reverse engineering by letting you take an existing database or script to build an Entity Relationship Diagram (ERD) of it. The ERD becomes the model of the original thing, which you can now improve upon.
You often look at examples before undertaking projects. Looking at a working ERD model of your business lets you find the things you like and dislike. MySQL Workbench builds the model for you ...