Hi there 

Thanks for posting your question in the Community! You can draw a line between ERD shapes by dragging a line out from a point on one ERD shape and attaching it to a point on another ERD shape. Once the line is established you can change the cardinality by selecting your preferred line endpoint in the dropdown menu of the toolbar.

To learn more about ERD shapes please review this Help Center article. Let us know if you have any additional questions!