The basic operations of the visual editor are available with your mouse buttons. Right click to start and create your first node. On the top of the editor you can get tips or errors for your current step. Left click is mostly used when adding scalars or connecting nodes to create mutation.
Obviously the best way to start is to open the tutorial. It will not only teach you the basics of the editor, but can also help understand GraphQL syntax. In this section you will create a simple schema with some common types and understand the basics of GraphQL. The red notes at the top of the editor are error notifications.
This way you can learn which concepts are handy and what to use.