Move your mouse to where you want to add a new section and click on "Add section here".

Select "Gallery and Slideshow" from the category menu on the left and choose a layout from the menu on the right.

Choose the gallery or slideshow you want in your new section.

Click on the section you just added to open the settings.

Click on the image to "add images".

Click on "Edit images" / "Add images".

Click on "Add images to the gallery".

Upload new images or select existing ones under "Recent".

The images in the gallery can be rearranged by dragging and dropping them to the desired position, then click "Done" / "Klar".