An Apple ID is essentially an account that allows a user to interface with all of the various Apple services such as the App store, iCloud, iBooks, etc. It consists of two parts: a user's email address and a password. An Apple ID is free to create and although it is possible to set up and use an Apple device without it, the user may be limited to the stock features which will severely limit the usefulness of the device.
An Apple ID can be created in one of three ways.
1. On a mobile device such as a phone or a tablet, simply navigate to the App Store and scroll to the bottom where it will prompt you to "Sign In".
2. On a computer, open iTunes (or install it first if it is not loaded on your computer). Click on Account in the top menu bar and select "Sign In".
3. On a brower, navigate to the Apple ID management site and click on Create Your Apple ID.
If you already have an Apple ID, you can choose "Use an Existing Account". Otherwise, click on "Create New Apple ID" where you will be led through a series of steps and questions. Enter the email address that you would like to use as your Apple ID. Be sure to choose your security questions carefully and to write down the answers. These will be needed in the event that you have forgotten your email address. The system will ask for a method of payment but you may choose "None" as an option. You will be asked to verify your account by checking your email for a verification email.
As a single user, it is unlikely that you would want more than two Apple IDs. Remember that you can only sign into any device with one Apple ID at any given time. Also, Apps that are purchased using an Apple ID can not be transferred to another Apple ID. Unless you have different roles that require different Apple IDs (e.g. personal account vs. an educational account), most users will want to stick with one Apple ID.
It is possible to change the email address that is associated with your Apple ID. Navigate to the Apple ID management site on a browser and sign in. You may be prompted for your security questions. If you have forgotten the answers, you will have to contact Apple Support for assistance in accessing your Apple ID. Once you have signed in, click on the "Edit" button next to "Account". You will see an option to Change Apple ID. Enter your new email address to make these changes.
Two-factor verification adds additional security to your account by sending a code to any of your current devices that is logged in with that Apple ID. You will need access to one of those devices in order to see the code that was sent. Using this code, you will be able to access your account.