One of my favorite tricks is to use Quick Look to view photos in a folder on my Mac. All you do is select the photo you want to view and press the space bar. The Mac will then give you a large Quick Look of that image. Press the space bar again to close it. It is simple and quick. You can then use the arrow keys to navigate through a folder while in Quick Look to view all the photos (this also works with most files).
But not only that, if you select multiple images in the Finder and hold down the Option key when pressing the Space bar, the Finder will run a full-screen slideshow with a 5-second interval between images! To display slideshow controls, move the cursor. This will also include a button to bring up an index sheet. This feature isn’t something most people need every day, but it can be a lifesaver when you need to run a quick slideshow at a party or presentation.