You will need the following:

1. An active MPN ID in the country location where you are onboarding to in Partner Center.
2. Global admin credentials for a Microsoft account.
3. A registered legal business name, address, and phone number for the country location you are onboarding.
4. An admin for the Partner Center account, if not the person who will submit the Partner Center enrollment for onboarding as an indirect reseller.

If you are not a Microsoft Partner yet and do not have an MPN ID, you can following the instructions here to join the Microsoft Partner Network.