By default, database security is turned off when you create a new database with PSQL v12. You turn it on by supplying a password for the Master user. See table Identifier Restrictions by Identifier Type for the restrictions pertaining to passwords.

PUBLIC is a special group because it provides default permissions for all users and groups. The database engine always checks permissions assigned to PUBLIC first. A couple of examples help clarify how PUBLIC permissions apply.

Suppose in PCC that you assign the CREATE TABLE permission to PUBLIC. You then create a user named myuser whose permissions in PCC do not include individual rights to create a table. Myuser can create a table because the database engine first checks default permissions in PUBLIC, and PUBLIC, in this case, grants rights to create a table.

Conversely, if a permission is not granted to PUBLIC, then the permission granted to the individual user or group applies. For example, suppose in PCC that you do not assign the CREATE TABLE permission to PUBLIC. No user can create a table unless the permissions for the user, or the group to which the user belongs, allow creating a table.

After you turn on database security, you can then define groups and users. Nodes for Groups and Users appear in PSQL Explorer in PCC. See User and Group Tasks in PSQL User's Guide.