How to Use Video on Google+ Overview:
2. In your “Share” box, select the video icon.
(Don’t bother with the Sharing prompts at this point ... It’s easier if you wait till the video has uploaded.)
3. A drop-down menu will appear. Select “Upload video”.
4. Add a caption to your Movie as it’s uploading
It takes a few minutes – even with a small movie. Just press “enter” when you've finished typing in your caption. (This will not affect the upload.)