Hmm! What happens when you left click on an empty cell (or one of the new cells that you've built)? Does a menu come up at all? If so, what's in it?
If you're building new cells, then the radial menus are at least partially working for you.
Edit: In case everything's working as intended, Exits live under the Resources submenu (they're where some resources come from), which the tutorial explains as seen below. The current active tutorial can be shown again by clicking the graduation cap icon in the bottom left.