How many groups of roles are supported in SQL Server ? Explain them

SQL Server uses roles. Two layers of access exist: access to the SQL Server and access to a database object within the server. Each can be configured separately.
There are four database roles, namely:
_ Public— Essentially anyone who has enough rights to connect to the database; the lowest role possible in terms of database permissions.
_ db_owner— Someone who has full rights to this database, including the right to delete it altogether, create objects, and so on.
_ db_data_reader— Someone who is allowed to read the data without any modifications, and who cannot create objects.
_ db_datawriter— Someone who is allowed to read and write data, but who cannot create objects.
These roles are contained in every database, including system databases. Every user will belong to at least one of them