5 minute data -- RRD 🔗 link

Hello,
 
I was wondering about the RRD database.
 
If I'm collecting 5 minute data, when does the
database begin rolling up the data (averaging it).
 
Does it keep a months worth of 5 minute data
and then does a daily average after a month?
Is there a process that compacts the database?
Just wondering how the process works.
 
Thanks...James