If you can’t see your desktop for all the open applications, just hold Command and Option down and click anywhere on your desktop. Press this combination to minimize the front app window to Dock, or press Command-Option-M to minimize all the windows belonging to the front app. Oh, and you can also press Shift-Command-G to move back to the previous mention. This means that if you use Command-F to find all the mentions of 'Command' on this page, and then tap Command-G, you'll be able to navigate through each one. Use it to navigate through each instance of the item you want to find. I'm sure you use Command-F to find items, such as words in a document or on a webpage. Or you can simply press Command-, (comma) to get to them in the fastest possible time. You can navigate to the Menu bar if you like and scroll through to access the Preferences. It works like this: You are working in an app, and you want to open the application’s Preferences. This is one of the least-known keyboard commands on a Mac, but it’s super useful. There’s also a keyboard shortcut - select an item (you can even use the Up and Down arrows to navigate to it in Finder view) and then press Command-Y.
To use QuickLook, select an item in Finder, press the Space bar and a preview will appear. A lot of people use QuickLook to preview items they're looking for.