Anybody can enjoy the content Khan Academy offers for free!
You can even use your Google, Facebook, or personal email account to sign up.
Having an account gives you the ability to track your own progress and earn points and badges!
For that, access https://www.khanacademy.org/ and click on the Sign-up option that best applies to will be your major role in Khan Academy - Learner, Teacher, or Parent.
Next, choose how you'd like to sign up - Google, Facebook or Email.
Learners younger than 13 years old do not need an email in order to have an account for privacy reasons and may simply choose a username and password directly.
Please note that users under 13 years old will also need to include their parent's/guardian's email here so they're notified of the account created.
If you are a parent or educator, also check out this article on how to create your own account and your child/students' accounts.