Hi there,
Basically you can add a new hard drive to any of the SATA Ports. It is probably better to connect them in sequence SATA0, SATA1 etc but you don't have to do this and quite often I connect drives where the cable routing looks the best. You may encounter a few issues if you try to install drives over 2 Gigabyte in capacity but, for now, lets assume they are 2 Gb or less.
In BIOS the drives will show up automatically if they are connected properly and the SATA port that the drive is connected to.
Now for the tricky part, if the drive is new, when you go into Windows it may not show up, this is because the drive will need to be formatted and assigned a drive letter for it to work within the Windows environment. To do this go to Control Panel/System & Security/Administrative Tools/Create and Format Hard Disk Partitions. When you open this tool it should recognize the new drive and tell you that it needs to be formatted. If I remember correctly it will probably say that first you need to initialize the drive by making it a simple volume. Format that drive as NTFS and assign it a drive letter this will usually be the next one in alphabetical sequence. The C: drive is the Main System Drive, D: drive is the DVD drive (if installed), so the next available slot will be E: