Create table group sub-folders in Management Studio
There is no way to create custom folders directly in SQL Server Management Studio.

Here are a few common strategies:


Group database objects by schema to help one-dimensional organization
Name objects from broad to specific areas


For the 1st option:

billing.Product
billing.Receipt
internal.Employee
internal.Office


Schemas are most primarily used to logical grouping of database objects, and can also provide an extra layer of security when using more than just the out-of-the-box configuration.  And the secondary benefit is, of course, the grouping of these items within SSMS Object Explorer.

For the 2nd route (name objects from broad to specific), it'd be something like this:

dbo.Animal
dbo.AnimalDiet
dbo.AnimalDietFootType
dbo.AnimalHabitat
dbo.Person
dbo.PersonAddress
dbo.PersonAutomobile
dbo.PersonAutomobileArchive


So on an so forth.  You can see that these objects alphabetically order themselves.  It's not just good for visual organization, but a great naming convention in my opinion.