1) You will need to get your authorization/EPP code and make sure the domain is unlocked. Both of these things will be done via the "Domain Information" icon.
2) You will also need to disable domain privacy (if you are using it) via the "Privacy Protection" icon
3) Make sure that your domains contact information is accurate via the "Contact Information" icon, then select the domain name
4) Once this has all been addressed you can start the transfer from the gaining registrars side and proceed with whatever instructions they give you.
The whole process may take 1 to 6 days to complete.