We can separate groups of tables into their own "namespaces", referred to as "schemas" by PostgreSQL. In many ways they can be thought of as being similar to directories, though that is not a precise description.
Make sure you've read the recipe Deciding on a design for multi-tenancy, so that you're certain this is the route you wish to take. Other options exist, and it is possible that they may be preferable in some cases.
Schemas can be created easily by using the following:
CREATE SCHEMA finance; CREATE SCHEMA sales;
We can then create objects directly within those schemas by using "fully qualified" names, for example:
CREATE TABLE finance.month_end_snapshot (….)
The default schema into which ...