Understanding My Server Folders And Hdd's?

OK another question now i've managed to get past my first milestone.
I need to understand how the storage works.
I've got a 250gb drive and 2 x 2tb in my HP N36L (the 250gb is the drive supplied as stock).
I've installed whs2011 and it's created to volumes C (60GB - 20GB used with the OS) and D 172.8GB (this is think is linked to the server folders as the free space is the same, client, docs, music, pic, rec, videos). then i've got my 2 x 2tb drives (1863GB) F and G below that that i mounted in WHS.

So in terms of what i'm looking for this to be, which is a simple media and document server anyway, before i realised this i created folders in F where i was going to store my data initially and use G for backups (but is this pointless?).

I've i start moving files from my other PC's to the server, will it max out at 172GB or will it then start filling up the other drives and i'll still just see the server folders i mentioned? How does it work? Is there something i should be doing to improve this?

I plan to install serviio and itunes at a later date when i've moved everything over.