While in a Zoom Meeting select the green Share icon with an up arrow at the bottom of your screen.  

A pop up will open asking you which screen to share (if you have multiple screens they will automatically be numbered for easy selection)

You can select the Advanced option to choose specific screen share features.

Select the screen you would like to share and click Share in blue at the bottom.

The screen sharing controls are now at the top of the screen that is being shared.  You will notice that the screen is highlighted by a green border. 

Press Stop Share when complete.