Navigate to your 'My Media' page. You will see your media arranged in a list. On the right side of the page, each entry will have a pencil icon 'Edit' button. Select this to edit the media. You will also find an edit button on any of page where you can view media that you own. It will be below the video on the right, in the 'Actions' drop-down menu.
Select the "Timeline" tab.
Watch through the video or move the playhead to where you want to place the first slide.
Click the bottom button, 'Create a new slide', on the left of the timeline.
The slide editor will appear. The following metadata can be added for a slide:
This is the display name of the slide
Slide Start Time
This is auto populated with the time the playhead was at when the 'Create a new chapter' button was pressed.
Enter a different time to change where the slide starts.
This is the displayed description for the slide
This is for comma separated search tags that apply to the specific slide content.
An uploaded image file.
Note: This must be an image file. You can output all slides from a
PowerPoint files as images by 'saving as' the presentation and selecting
an image type from the 'Save as type' menu. It is recommended to use the 'JPEG File Interchange Format (*.jpg)' option.
Once the relevant metadata has been entered and a slide has been uploaded, click the '+ Save' button to add the slide to the timeline.
After saving the chapter, you may move the playhead and continue adding slides or click on existing slide icons in the timeline to edit them.
Note: to delete a slide, click on it's icon and select 'Delete Slide' below the '+ Save' button.