In order to add a watermark to your videos, head over to the step "Watermark" and upload the image you want to be displayed as the watermark.
Once your logo is uploaded, you can simply click on it, and it will appear on the canvas. You can then reposition it by dragging it along the canvas.
You can also just delete the watermark by clicking the X sign.
You can add several watermarks that will be displayed simultaneously on the canvas.