These tips both involve your PREVIEW program.
If you want to watch a slide show of a group of photos or just a collection of images. Hold down SHIFT and click on the images you want. They don't have to be in any order and you can skip some if you want.Thn
Hold down COMMAND + OPTION + Y all at once and your slideshow will pop up.
Here's a link that tells you more about the slideshow.
When you double click on a graphic or photo you can see it in PREVIEW. That's not too exciting. However if you click on the TOOLS dropdown menu you 'll find ADJUST COLOR. Clicking on that will open a whole picture editing tool.
With the editing tool you can
- lighten or darken
- add contrast
- change tint
- add saturation
- make into a Sepia image
From the menu above the photo you can