Manual of registration process for enrolling in to GST has been put into Public Domain. Click the link below to access the registration Process
Enrolment of Existing Taxpayer with Provisional ID and Password:
Normal Taxpayer:
https://tutorial.gst.gov.in/userguide/registration/#t=Apply_for_Registration_Normal_Taxpayer.htm
GST Practitioners: https://tutorial.gst.gov.in/userguide/registration/#t=GST_Practitioner.htm