One of the things I like about the Mac is that it's easier to figure out what applications are queued up to start when you start up your system, though, like Microsoft Windows, there are still additional programs and helper apps that launch invisibly. Often those are the cause of slowdowns and slow boots, too, which is a drag, but that's another topic. What you seek, having a Mac app like iTunes automatically start up when you boot your computer, is done through a System Preference...

To get there, let's start from the most basic step, and you'll see, we hit a hiccup along the way because by default my computer is configured to not log in to a user account on startup: you can't launch user apps unless you change that. Don't worry, if you start up your computer and then have to enter an account password to go further, then you'll either need to change this (I'll show you how) or accept that it will launch when you log in rather than just start the device.

First things first, though. You'll want to find the Apple menu on the top left and choose "System Preferences...":

When you do that, you'll see that there are a ton of different preferences you can set and modify. We're just interested in one, however, about 2/3 of the way down on the window, "Accounts":

Click on that and you'll see what user accounts you have set up on the computer. It's a great idea, by the way, if you do have more than one person using a computer to set each up with a different account., which you can do by simply clicking on the "+" button below the list of users.

See the padlock on the bottom, though? If it's closed -- as mine is -- you need to click on it and enter your admin password so you can make changes:

Once you've done that, click on the "Login Options" to find out whether you have autologin set or not:

You can see on the top there that Automatic Login is set to "Off". You can leave it that way if you want to just have iTunes launch when you log in, but if you do want to have everything happen automatically when you restart then click on "Off" and get the menu to appear:

I'll chose "Dave Taylor" but I'm just guessing here that you have something else in the menu. If you too have "Dave Taylor", well, um, hi brutha!

Now click on your account name on the left side and the autologin changes (if any) will be saved. Now you'll see this again:

This time you want to click on the "+" button roughly in the center of the window to add a new app to the autolaunch list. Now, find the app you want to include (iTunes):

Looks good? Great, just click "Add" and iTunes is now added to your Login Items list, to be automatically started up each and every time you start up (or log in to) your computer:

if you ever change your mind, btw, click on the item to highlight it, then click the "-" button to remove it from the list. It will never delete the app from your computer, just remove it from the list, so you can change your mind again and put it back at any time too.