If you would like to use Halaxy in different practices without sharing information between them, create a new account for each practice using a different email address (you can use the same password). Each practice will not be aware of the other one, and there is no sharing of information (such as calendar and patient information) between the different accounts.
Note that a single Halaxy account can be part of multiple practice groups, with completely separate data for each group. Please see this related article on how to set up a new practice group and how to switch between practice groups.
If you would like to share information between your practices, you can add a new location instead of using a new account. The new location is still considered part of the same practice group and will share many of the same settings, although you can add location-specific invoice templates and separate bank deposit details for receiving payments.
When adding practitioners to the new location, you should check that their access level is appropriate for your practice.