For drawing complicated molecules, you can use the Drawing tool, which enables you to create bonds without changing tools or even releasing the mouse button. For more information, see Bond.
You can find more functionalities in context menus. You can open context menus by right-clicking on certain parts of your structures (for example atom, bond, R-group definition, and so on). For more information, see Context Menus.
By using the options available in the View settings it is possible to specify how structures are displayed. For more information, see View Settings Dialog.
You can get more information about the other features of Marvin JS from the Marvin JS Video Tutorials.