Each user of database (unless he/she is read-only user) can give rights to read/modify his/her items to other users.

You see from quick-selection menu we can choose Public - in this case item will be accessible by any user in the database, or Private (default status)- this item will be accessible only by creator (except SYSDBA and any super-users).

We can also limit access to this item by "Read-only" property.

If we want to assign access to this item to specific users, let's press the "..." button. There you can select specific users, or select "All current and new users" - that's Public status.