An Apple-ID is required to sign-up to the Apple Developer Program.
If you already have one, scroll down and go to the next step "Enrollment / Account creation".
1. Open https://appleid.apple.com/account
and fill out the form
2. Once the Apple ID has been created, you will receive a verification email. Copy the code received and continue.
3. You will be asked to log in again, so use the email and password of the Apple ID you have just created.