So although there may be a number of people creating tables in a database each user will see only their own and the DBA's. It is good practice to name objects meaningfully and use your initials at the start to ensure a unique name. If you create an object other than a table eg a report or a form with the same name as one owned by the DBA, this will make the DBA's object seem to disappear because it is hidden by your object of the same name. If you remove your object the DBA's will be visible again. There is one variation on this situation with regard to applications.
All users can see the names of applications created by all other users in a database.
This can mean that the application catalog becomes large and takes time to scroll through to find your application. Do not create applications with silly names or comments that will annoy others. For group projects special permissions can be granted to allow a number of users to appear to be the DBA and hence work together. What you should use Databases for Databases are created for specific courses and projects. We do not keep databases indefinitely and you should not keep data on one subject in a database intended for a different subject.