How to add a new drive to my server

Hi,

I have an HP ProLiant ML350 G6, in the front HDD rack i have some unused slots and i would like to fill them up with some new drives. How do i do that? I don't have a "cage" where to put a standard 3.5" drive, so i wonder if i need to buy the whole cage+drive package.

Also, can i organize the drives in any way i want, making more than one RAID volume with a single rack and a single raid card? i guess yes, but i would like to be 100% sure, as i don't have experience in this field