SCID allows you to have many open databases at the same time.
Whenever you switch between them (via [TheDatabaseSwitcher] or [TheFileMenu]), the [TheActiveGame] changes.
The concept of active database refers to the one in which [TheActiveGame] resides.
Adding, saving, or replacing games is done in [TheActiveDatabase].
See [TheConceptOfActivity] for more details.
Wiki: HowToCreateDatabases
Wiki: HowToImportGames
Wiki: TheActiveDatabase
Wiki: TheDatabaseSwitcher
Wiki: TheEditMenu
Wiki: TheFileMenu
Wiki: TheGameMenu
Wiki: TheSearchMenu
Wiki: TheTreeWindow