Floors and reference planes are used to help the designer model elements at the correct heights in the model. In this video you will learn how to set the active working plane and activate the appropriate snap locks.
If you would like to work hands on with the videos please visit the Bentley Learn Server and download the dataset from the course 'Learning OpenBuildings Designer - Modeling and BIM Essentials'.
https://learn.bentley.com/app/Public/ViewLearningPathWithMasterCourseExpanded?lpId=116818&mcId=103962