You can access the Content Manager of any Instance from the Instance Setting drawer by the blue "Open Content Manager" button, as shown below. Once selected, you will be redirected to your dashboard that provide a complete overview of your project.
Inside the dashboard you are provided an overview of your instance. The overview includes:
Quick access links to your live & dev domains, Instance settings, favicon setup, navigation to various content management sections and their documentation, and any open work tabs
Content of your project grouped by relationship within the content section, parentless data models under headless content models section, platform navigational sidebar, quick content model create and search
Latest edits and published content with links to the corresponding content model and content
Overview of work completed in the last 30 days, breakdown by day, recently edited sections for easy workflow continuation
From here you can begin creating content. Up next is a complete breakdown of the types of content models available and how to utilize them.