The following steps summarize to transfer domain from person to another:
1: Log-in to your registrar user account.
2: Access your domain list.
3: Access the change account details / transfer domain feature (different depending on registrar).
4: Enter new owner account details, including the email / username of the new owner.
5: Complete the transfer request.
At this point, your registrar sends an email notifying both parties of the transfer initiation. The email sent to the new owner usually contains a set of security keys combined with other information related to the domain transfer.
To complete the transfer the new owner follows the steps outlined in the email sent by the registrar.