Add programs to the Dock
When you first get your Mac, or create a new user account for it, the Dock greets you with Apple’s predefined choice of which apps it believes you will be happy to see there. Unsurprisingly, they’re all Apple’s own, and although you may be using most of those as a matter of course, you will undoubtably want to add other apps and even folders or files to it, and remove those who get in the way.
Notice the faint line somewhere to the right of the dock – to the left of that line is where the apps go. Folders and files can be added to the right. Adding anything to the Dock is easy: drag whatever you wish onto it and as long as it’s on the correct side of that line, the other icons will make room for the new addition. The more you add, the smaller the Dock gets as it’s limited by your Mac’s width.
Another way to add a new program to the Dock is to open the program, and once you can see the icon in the Dock, right click and choose Options > Keep in Dock.
Read how to customise your Mac here: How to customise your Mac desktop
Remove programs from the Dock

If your Dock’s getting too crowded, it may be a good idea to remove some items from it. You may find that dragging them away from the Dock, merely gets them to snap back to their position in the Dock, but that’s because you’re not dragging them far enough away: click on the icon and keep dragging up until you need a small puff of smoke beneath your cursor, then let go.
Alternatively, control-click on an icon to reveal a menu. Mouse over ‘Options’ to open a submenu and select ‘Remove from Dock’ from there.
Reorder icons in your Dock

Now that you’ve got all the apps, folders and files you want in your Dock, it’s time to reorder them anyway you like. The only two that are immovable are the Finder and the Trash which must stay on the left and right sides of the Dock respectively – they’re also the only two icons that cannot be removed. Aside from that you can move an icon and reposition it by dragging it anywhere on the Dock.
Make Dock icons bigger with magnification

If you have many icons on your Dock and you find it too small to see, you can activate Magnification, that way, whenever your mouse is over it that part will swell up, making it easier to click on the right icon.
You can switch it on and off in the Apple Menu, top left of the screen. Click on it then go to Dock > Turn Magnification On.
Controlling the amount of magnification is done with the help of a slider in the System Preferences. Read our Tips for using System Preferences in Mac OS X
Move your Dock to the side

The System Preferences’ Dock section offers a host of other options to help you customise the Dock to suit your needs. You can control its size with a slider just above the Magnification one.
Be aware though that the number of icons present in the Dock may supersede your request. It’s also possible to position your Dock elsewhere on the screen.
Since our screens are wider than they are tall, a Dock could be less obstructive if it were on the left and right of it and the option is there for you to choose (you can also do this from the Apple Menu).
Turn off Genie Effect in the Dock

By default, when you click on the green button of any open window, it will get sucked into the Dock. The squeeze effect you’ll see (which you can slow down by holding down the Shift key) is called ‘The Genie Effect’.
You can change that visual style from the System Preferences by clicking on the ‘Minimise windows using’ menu and choosing ‘Scale effect’.
As mentioned, minimising windows will get them sucked into the Dock, but if you’d rather have them disappear into the app’s icon in the Dock, tick ‘Minimise windows into application icon’.
Hide an app in the Dock

The Dock is not merely a repository of apps, folders and icon – it has a few other features built in which you may well find very useful.
For instance, you can hide a program with it. Hiding a program isn’t quitting it: all windows and any unsaved work is still open and exactly where you left them on the screen, but hiding it makes it all invisible, enabling you to focus on another task should you need to.
In order to do this, click and hold on a running app (one that has a small white line underneath it – unless you removed that visual clue through one of the System Preferences’ options). At the bottom of the list is the Hide command.
You can also access this menu by right clicking on an app icon in the Dock.
Force Quit via the Dock

Although it isn’t as bad as it used to be, we sometimes still encounter unruly apps which won’t behave: every time the cursor goes over them, it changes into the dreaded spinning beach ball. When that happens, force quitting it may be your only option, and you can do this straight from the Dock: click and hold on its icon to reveal the menu mentioned above.
If you then hold down the Option/Alt key, Quit will change into Force Quit, enabling you to get rid of that app and hopefully everything will be fine the next time you launch it.
Open a file in a different app

When you double-click on a document, it opens in the app that created it. But sometimes, you may want to open it elsewhere. For instance you might like to work on a file you created in TextEdit in Pages.
In order to do this, drag its icon from the Finder onto the Pages icon in the dock to make sure the right app is launched for your needs.
Plus: Dragging a file into Mail’s icon will add it as an attachment in a new email message – which is a great time saver.
Empty the Trash via the Dock

Finally, we’re left with the Trash. This is the one icon that can’t be found anywhere else on your Mac. You can empty it from the Finder by going to the Menu Bar, clicking on Finder and choosing Empty Trash, but it’s also possible (and far quicker) to perform this action by using the Dock.
Click and hold (or right-click) on the Trash to reveal a menu; select ‘Empty Trash’ and you’re done.
Those the more security minded among you, hold down the Command key and ‘Empty Trash’ will turn into ‘Secure Empty Trash’, where the data is overwritten before being deleted. There are other customisable features to the Dock, but we’ll have to leave those for another time.
Read: Best free Mac Apps