The registration site is here.

The registration includes a nominal fee ($10 for students and ACM members and $30 for non-members). After October 20, the registration fees for non-students doubles (to $20 for ACM members and $60 for non-members); student registration fees remain $10.

If you are unable to cover the registration for any reason, you can apply for a registration waiver here and you will be given a code to reduce your registration fee to $0.