The NCAA has an informational page available to student-athletes who are contemplating a transfer. It can be found here. Beginning in October of 2018, the NCAA created what we now know as the transfer portal and changed the rules for transfer eligibility. The portal enables players to register themselves as being eligible for and potentially desiring a transfer. Registering does not mandate that a player must ultimately transfer. Additionally, there is no separate requirement to get permission from the current school in order to make the move.
One of the biggest effects of the new system is the very public nature of putting one’s name on the portal.