With slideshows you're able to insert several photos on one place. It'll automatically rotate through a series of photos.
If you want to add slideshows in the Visual Mode you can click on "Slideshow" in the right rail. Now you'll go to a screen where you can upload a photo to the slideshow. Upload a photo or choose one. At the end you can change the settings of the slideshow. You can change for example the size and the position
You can use the following codes to add slideshows on your wiki:
<gallery type="slideshow"> Photo.png|Describing|link=Link Here|linktext=Text to Display for Link </gallery>
<gallery type="slideshow" widths="200" position="center" crop="true"> Photo.png|Describing|link=Link Here|linktext=Text to Display for Link </gallery>