sweetie,

By any chance you have Enterprise Manager. If you open DBA studio and select schema view 'by object' and 'by schema' you can see the difference with your eyes. Even if you don't have OEM set up for your enterprise, you can set up OEM client on your terminal and login locallly without Management server.

AFIK, Schema can be mentioned in terms of 'Ownership'. Unless otherwise the user creates objects, user can't be owner of those objects. User might be having equivalent permissions of Owner(select,insert,update,delete) on other's objects, he can't be owner of objects.

So, to my understanding:

schemas are collection of objects that are created by an user?

NOT

schema forms the group of objects that an user can access including objects not created by the user.