To view a slideshow of images:

Open the first image in Preview.

Choose View > Sidebar.

Drag the other images from the Finder to the sidebar.

Select the first image.

Choose View > Slideshow.
You can display a slideshow of all the images in a window. The contents are displayed using the full screen, and controls at the bottom of the screen let you move from image to image or end the slideshow.
Open the first image in Preview.
Choose View > Sidebar.
Drag the other images from the Finder to the sidebar.
Select the first image.
Choose View > Slideshow.