When creating an Apple ID from scratch, you'll have to click through a few screens to begin entering your information. Among these is a screen that asks you to agree to the iTunes Store's terms. Do so.
At the next screen, enter the email address you want to use for this account, create a password (iTunes will give you guidelines on creating a secure password, including using numbers and a combination of uppercase and lowercase letters), add security questions, enter your birthday, and decide if you want to sign up for any of Apple's email newsletters.
You'll also have the option of including a rescue email, which is the email account that your account information can be sent to if you lose access to your main address. If you choose to use this, make sure you enter a different email address than the one you use for your Apple ID login, and that you'll have access to it for a long time (since a rescue email address isn't useful if you can't get at that inbox).
When you're done, click Continue.