If you re-install BOOK|IT on the same computer your schemas will remain. However, if you deinstall BOOK|IT on your computer and then install it on a different computer, they will not be there anymore.
When you want to create a new BOOK|IT schema you go to the list of BOOK|IT schemas via BOOK|IT schemas in the navigation bar. There you click on New schema.
You will get to the BOOK|IT wizard. The wizard will help you with creating a schema. Click on Next. You can find out how to choose the name of the schema and a sync direction in the chapter Name of the schema and sync direction.