For your Apple ID account, you have a primary e-mail address and alternate e-mail addresses. Your primary e-mail address is the one you use to sign into itunes and anything else requiring that you sign into your apple ID. This cannot be changed. However, your alternate e-mail addresses can be added, changed, or deleted. Also, the e-mail addresses that you use for face time can be added, changed, or deleted.
Hope this helped!
CamilleMacBook, Mac OS X (10.6.8)
Please don't confuse the Primary email address with your Apple ID. The primary and secondary email addresses are linked to the Apple ID, and Apple recommends the primary email address match the Apple ID, but the Apple ID itself is really just an account name. In the past, they used to allow non-email type IDs, now they want all Apple IDs to be email addresses. You actually login with your Apple ID not your primary or additional email addresses.
question 2: How do I get an Apple ID?
You may already have an Apple ID, and you only need one for everything you do with Apple. If you aren't sure, visit My Apple ID and click "Find out."
If you don't have an Apple ID, you can create one at My Apple ID. You can also create one by signing up for an Apple service (such as an iTunes Store or iCloud). You should use your primary email address as your Apple ID.
Note My Apple ID is also where you can login and manage your account. There's a "Manage your account" link on the right.
A lot of information about Apple IDs can be found at Apple ID Support where you can select the different headings on the left and read all about it.
An issue some people have is they have an Apple ID that is an email address. That email address gets outdated and they no longer use it. But instead of renaming the Apple ID, they create a new one. If they have purchases and important stuff with the old Apple ID, this causes confusion and issues. If your Apple ID is not an @mac or @me Apple ID, it can be renamed, "How to change the name you use for your Apple ID".
It's recommended to stick with one Apple ID.
You can't delete an Apple ID once it is created. What you want to do is rename the old Apple ID to the desired name without creating a new one. That way you don't loose your old purchases or anything. It's the same account but with a new name, a new "ID".
I encourage you to check out the Frequently asked questions about Apple ID