Adjust the templates and styles in the Site Editor.
Add Users
Open Users > Add New User to create new users
Add Pages
Open Pages > Add New Page to create any missing pages like Terms and Conditions, Privacy Policy, Contact Us, etc.
Bulk-Import Posts
Open Post Management to add posts via the API-driven importer.
Edit Content and add comments
You as the admin (and depending on the user role even others who have access to the site) can always modify the content in real-time from the frontend.