If you need to show someone a screen, but you're not on a Biba call, or if you're just using the conference bridge for your call, you can still share your screen from the desktop app with just a couple of clicks.
From the Home Page, select Start Meeting (or from the Launchpad, go to Meetings > Start a Meeting)
Choose whether you want to use your own PIN, or a one-time PIN, then click Screen Share Only
Your screen will immediately be shared, and you will be placed in the Call Roster. Click to copy the screenshare url at the bottom of the screen, then email or message it to your callee, and they can view your shared screen in their browser.
You'll notice that there's no microphone next to your name. Because this is a screen share only session, there's no audio.
You'll also notice there's a new Audio button in the call controls. This will allow you to add audio to the screen share session, and turn it into a full meeting.