There is the database writer called dbw0. Previously this was known as dbwr. There is also the log writer which writes to the redo logs. Pmon is the process monitor. Finally the archiver copies online redo logs to secondary storage (disk).
Obviously there are a lot of other background processes that make up the database instance. I am not as interested in them as I am a PL/SQL programmer, not a DBA. Next time I will go over simple ideas such as triggers and users.