Photos is very different from iPhoto. Nearly all support for projects (Books, Calendars, Cards, Prints) has been removed from Photos and delegated to third party extensions. Slideshows are the only projects, that have been left, but the support is limited and there are some bugs, if we include videos into the slideshow.
We do not have much control over the layout in a slideshow with several photos on a slide. Basically, select the photos you want to present and create a slideshow project with "File > Create > Slideshow > Photos". Use the controls to the right of the slideshow window to select a theme and a sound track. Trying to rearrange the sequence of photos on the individual slides is like herding cats, as Photos will rearrange them again to fill the templates. If you want the Live Photos to play and to include videos, consider to create a Memory instead of a slideshow. Memories are the only type of presentation, where at least some of the Live Photos will be animated.
In addition to watching the video pointed out by Yer_Man you may want to look at the user guide: Create slideshows in Photos on Mac – Apple Support (UK)