An Apple ID is your user name for everything you do with Apple:
Shop the iTunes Store, enable iCloud on all your devices, buy from the Apple Online Store, make a reservation at an Apple Retail Store, access the Apple Support website, and more. (from Apple website)
Apple ID Support (from Apple website and your best bet to get it done right)
http://support.apple.com/kb/HT5622 then to "Manage your Apple ID"
Is there a way to find my Apple ID Name if I can't remember it?
Yes. Visit My Apple ID and click Find your Apple ID. See Finding your Apple ID if you'd like more
How do I change or recover a forgotten Apple ID Password?
If you've forgotten your Apple ID Password or want to change it, go to My Apple ID and follow the instructions. See Changing your Apple ID password if you'd like more information.
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 your Apple ID.
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.
You do not need to create a separate Apple ID for each Apple service. A single Apple ID can be used to access all other Apple services.
I have multiple Apple IDs. Is there a way for me to merge them into a single Apple ID?
Apple IDs cannot be merged. You should use your preferred Apple ID from now on, but you can still access your purchased items such as music, movies, or software using your other Apple IDs.
Other sites that are helpful for Apple ID and Password information:
APPLE ID & PASSWORD