Apple - How to start a slideshow on the Mac quickly and easily?

In Leopard and later versions (up to El Capitan), select the files you want in the Finder and press the spacebar to invoke QuickLook. You can then use the arrow keys to cycle through them. If you click the full-screen icon, Finder and QuickLook displays the slideshow. You get extra animation in some os versions if Finder is showing files in cover-flow layout.

In OS X Yosemite 10.10 and later, the maximise (full-screen) button is in the upper left-hand corner. Then press "play" to start the slideshow.

For OS X 10.9 to 10.7 the full screen icon is top right.

In Tiger, there is a "Slideshow" option in the context menu in the Finder.

In Panther and earlier, it is indeed several steps before you can get a slideshow.

Select a picture or group of images from the desktop, then use the following:

• Option+Spacebar to launch image(s) into the full-screen slideshow mode
• Spacebar to pause/play the image slideshow
• Left Arrow to go back, Right Arrow to go forward
• Gesture with two-fingers left to go forward, two-finger gesture right to go back
• Option to view smaller images at actual size
• Click “Index Sheet” to view thumbnails of all images in the slideshow
• Click “Add to iPhoto” to import the image into iPhoto
• Hold Control key and use a two-fingered back or forward swipe in to zoom into the photo
• Escape to exit

If you use OS X "Quick Look" you can use right/left arrow on the keyboard and view all of the photo on the same path; but you have some problem yet, "Quick Look" let you view all the file exist in the same path not just photo.