Okay... here we go with some info about Oracle backups.
COLD BACKUP
Usually database is in noarchivlog mode; no point in time recovery.
You shutdown your database then you copy -operating system copy - all your datafiles, control files, etc.
If you have to restore you just copy everything back and startup your instance.
HOT BACKUP
Usually database is in archivelog mode; allows for point in time recovery.
You put your tablespaces in backup mode then copy all your datafiles and archivelogs -operating system copy - plus you create a control file and copy it too.
If you have to restore you copy everything back, startup nomount your instance, rollforward archivelogs and then open your database.
RMAN
Allows for point in time recovery and database clonning.
This is Oracle's native backup tool, imposible to tell you in five lines all RMAN is capable to do but think RMAN knows everything about your database and you just have to tell it what you want to do either backup or restore.
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Pablo (Paul) Berzukov
Author of Understanding Database Administration available at Amazon and other bookstores.
Disclaimer: Advice is provided to the best of my knowledge but no implicit or explicit warranties are provided. Since the advisor explicitly encourages testing any and all suggestions on a test non-production environment advisor should not held liable or responsible for any actions taken based on the given advice.