How to create an Oracle 11g user with read access to all tables/schemas

The last two entries have unbalanced parenthesis. You're not closing the top-level parens.

TEST =
  (DESCRIPTION =
    (ADDRESS_LIST =
      (ADDRESS = (PROTOCOL = TCP)(HOST = localhost)(PORT = 1521))
    )
    (CONNECT_DATA =
      (SERVER = DEDICATED)
      (SERVICE_NAME = Test)
    )
  )              -- add this
med =
  (DESCRIPTION =
    (ADDRESS_LIST =
      (ADDRESS = (PROTOCOL = TCP)(HOST = localhost)(PORT = 1521))
    )
    (CONNECT_DATA =
      (SERVER = DEDICATED)
      (SERVICE_NAME = med)
    )
  )              -- add this

(Don't add the comments though.)

Might be a good idea to be consistent with casing everywhere (even though I'm not sure it actually matters). If you call your database TEST, put TEST everywhere, not Test in some places and TEST in others.

In order to do RMAN backups you need the SYSDBA or SYSOPER roles. In order to grant those you need to be able log on as a user with those roles: ie the SYS role.

There are variations where you use OS authentication or if your OS user is a member of the ORA_DBA group.

Easiest is if you can do this:

CONNECT / AS SYSDBA

from the server then you can run an RMAN script like

RMAN> BACKUP AS BACKUPSET DATABASE PLUS ARCHIVELOG;

This very basic script should be configured with details particular to your setup such as the location to backup the files to, crosscheck existing backups, etc.