Oracle Database Discussions

Hallo!I am trying to better appreciate Oracle backups in terms of datafiles,redo-log files and archive log files.My questions are as follows

1)When database transactions are committed,they Log Writer saves the data in the redo-log files.At what point is this data also saved in the datafiles by the database writer?

2)Can datafiles stored on disk but not yet backed up via an offline backup be used in recovery of the database?I am assuming one does a scheduled offline backup daily at night when users are not around.Then users create extra transactions during the day.A media failure occurs.One does a recovery of the database.Will the data recovered be only upto the last backup or will the datafiles containing data from that day’s transactions also be used in the recovery?

Thanks.