Each project represents a database. Projects can be used to organize different application schemas or environments.
Directus allows for one instance of the API/App to manage any number of project databases. Each project has its own database and is configured in its dedicated API config file, where all options can be configured.
As of now, this can only be done manually.
Since Directus is multitenant, you need a way to link to specific projects. This is accomplished by adding a project query parameter to the login page containing a base64 encoded URL of the API you want to use, the application will automatically select "Other" (if allowed) and pre-fill the API URL.