To enable control sharing in a meeting, simply click on the Share control button in the host menu bar:
Once the control sharing button turns green, your participants can fully control mouse and keyboard, therefore use your webapp like it would be displayed on their local browsers.
In meetings with more than one participant, you can also selectively share control with just one person. Click on the participant list and for the person you wish to share control with, click on the arrow symbol next to their names:
Once the arrow turns green, your participant has full control over the screen share.