SaaS 2.0 build on a special k8s library so depends on the port you want to open then the first login will ask you like the images bellow.

Odoo SaaS 2.0 Frist login welcome screen

Odoo SaaS 2.0 Frist login welcome screen

After login you will be direct to admin panel => then you need to navigate to Global => SaaS => Default where you start to wok.

Odoo Saas 2.0 admin pannel

Odoo Saas 2.0 admin pannel