How can I create a new showreel?
In the menu, click on "Manage media" and then on "Showreel Manager".

Click on "+ New showreel" on the right-hand side above the video library:

In the window that opens, you have the option of entering the title for the showreel as well as making further specifications regarding the visibility of the showreel and uploading a preview image:

Please note:
If you are not a Premium member, you will only have limited configuration options for showreels; advanced options such as preview images or the download option are only available to Premium members.