Start by reading the actual regulation, provided here in a easy online format without the extraneous formatting: https://gdpr-info.eu/

If you want a shortcut, you can try the EnterpriseReady site which has a great overview specific to SaaS companies: https://www.enterpriseready.io/gdpr/

As always though, your best resource is to talk to a lawyer. Do not trust any internet comments about legal decisions for your business.