To create your first watermark please go to the watermarks dashboard page.
While there, click on Create Watermark button in the top right corner.
Please select some transparent PNG or JPG file to upload as a watermark.
Here you can enter a unique name (id) of your watermark (that you will use later as on option on your images & videos so chose something that you will remember), together with the desired position of the watermark. (default is bottom-right), while the padding is optional (and will move the watermark number of pixels from its position).
For a full list of options read watermarks documentation