Hand histories imported into HM3 and all related information is stored locally and contained in a single file database. By default, databases are stored in a Holdem Manager 3 folder in your Documents: C:\Users\_USER_\Documents\Holdem Manager 3\Databases. If you can't see it, turn off the windows option that is hiding that directory.
File > New database to create a new database*.
File > Open database to open a different database.
File > Recent databases to choose from recently opened databases.
Databases can only be moved or copied while HM3 is closed. Sharing HM3 databases between multiple computers or synchronizing them to the cloud storage while in use is not possible and will corrupt the database.
*Please do not create your HM3 Database in a sub-folder of any cloud file hosting service (Dropbox, OneDrive,.Google Drive, etc) as it can cause database corruptions because it will constantly be syncing the database to the cloud while you are playing/importing.