Aadhar Card Online Appointment facility is started on trail basis all the enrollment centers do not have online enrollment facility so you have to check whether the enrollment center near you has online appointment facility. You can check nearby enrollment center by visiting the link https://appointments.uidai.gov.in/easearch.aspx .

Aadhar Card Online Appointment

If  the enrollment center has online appointment facility then visit the link https://appointments.uidai.gov.in/ and fill the form you will be given an appointment according to your date and time filled by you.

Appointment for Aadhaar enrollment

If the center near you does not have online appointment facility you have to visit there without an appointment and fill the form.