There are two different ways to upload already existing video files:

Upload from the New Session page (only allows one video file to be uploaded at a time)

Launching the Editor in Composer Mode (allows for multiple video/presentations files to be uploaded)

How to Upload video files from the New Sessions page:

Click All Folders or My Folders on the left hand column and choose the Folder where the session will be created

Click the Create option on the top panel after choosing your folder

When you click create a dropdown menu of options will appears.  For uploading video you will choose the Upload video option as seen below

Under Actions – drag and drop in the video file or click Browse to select the file.

New to 4.5 – You can now drop multiple files into the video upload window at one time to create multiple sessions!

Wait for Uploading/Processing to finish (may take awhile based on the size and amount of files).

Uploading:

Processing:

Once processed, the session can be edited right away. Once the publishing completes, you will be notified that it is safe to close the window and perform other tasks.