The Show a Part of Your Screen option displays only a specified area of your desktop. When selected, Live View will open a movable and sizable display window headed with the orange top bar. At launch, the Live View session will be paused; simply move and re-size this window to the area of your display that you would like to let others view and click the Resume Live View button to begin transmitting to your viewers.

All Live View sessions will feature an orange bar across the top bearing the display name of the initiator, as well as, the Live View and window control tools. The Live View control tools enable you to share, pause and resume transmission of the Live View image. The window control tools enable you to minimize, restore, maximize and close the display window.

The Part of Screen option is useful when there are things open on your desktop that you may not want displayed to others in the meeting. You can keep these things “off screen” for the others in the meeting.
If a viewer’s desktop size is set to display fewer pixels than yours (i.e. yours is set to 1024 x 768, while theirs is set to 800 x 600), it may happen that the Live View will appear on the viewer’s screen with scroll bars to enable viewing of the portion of the image that could not be made to fit.
Once a Live View "Part of Screen" session has begun, you may move or resize the active Live View window as often as you like, and only the contents of this window will be displayed. Your viewers may also move and resize the Live View window to the position where it is convenient for them, but their window will only show an image of the exact size and shape as yours. As a viewer, if you choose to resize a Live View window larger that the Initiator’s size, then you will see that the surrounding space is blacked out. If your Live View window becomes smaller than the Initiator’s window’s size, you will at first only be seeing the upper left portion of what they are displaying, and you will have scroll bars available to allow you see the rest.
As a viewer of a Live View "Part of Screen" session, you may notice that there are two mouse cursors; yours and the initiator's. The mouse cursor of the initiator of the Live View session will be visible whenever it is within the session's display area, and can be used by the initiator like a laser pointer to call attention to specific areas of the Live View image.