Folders on the Mac: those you see in the Finder and via Open and Save dialogue boxes have sidebars which I often describe as functioning ‘like a Dock for windows’ (the Dock being that strip of launch icons normally along the bottom of your screen, or maybe on the left or right depending on your Preferences).
If you can’t see this left-side Sidebar, click View from the Finder menu and select ‘Show Sidebar’. If you want to get rid of it, while it’s visible the same menu item becomes Hide Sidebar.
1/ Add a folder to the favourites section — If you have a personal folder you’d like to appear in the sidebar, just select it with your mouse and drag it to the Favorites (sic) section of the sidebar — and when you do, make sure to place it between a pair of existing Favorites folders rather than inside of of them.
2/ Remove a folder from your favourites — Right-click (or hold down the Control key on your keyboard and mouse/trackpad-click) the folder you want to un-favourite, and select Remove from Sidebar.
3/ Customise the Sidebar items — Since Sidebar items are actually just shortcuts leading to real items (ie, like the Dock), in addition to key directories like your Applications and Movies folders, the sidebar can also display hard drives, DVDs, connected Internet servers and file ‘tags’ (which first appeared on OS X Mavericks), and other items.
To add or remove any of these items, click your desktop to make the Finder menu appear at the top of the screen, click the main Finder menu, select Preferences, click the Sidebar tab, then check or uncheck the various sidebar item options as you see fit.
4/ Rearrange your favourites — Just click, hold, and drag up or down to rearrange items in the ‘Favorites’ list of your sidebar. Make it work for you – that’s what your Mac is all about.
5/ Make the sidebar bigger, or smaller — Grab the sidebar’s right edge with your mouse and drag it one way to expand it, or the other to shrink it.