You need a place to mount to. That is called the mountpoint. Create a mountpoint like this:
mkdir /media/mystuff <-- Call it anything you like
At this point you can mount the partition manually, like this:
mount -t ext3 /dev/sdb1 /media/mystuff
The partition should be mounted and available by browsing to /media/mystuff. It will remain mounted until you manually unmount it (umount /meda/mystuff) or you reboot. To have it mount automatically, at boot, add an entry in /etc/fstab, like this:
/dev/sdb1 /media/mystuff ext3 defaults 0 0 (Pay attention to the spaces in this line).
The partition will then mount automatically whenever you boot your system.
You can't mount /dev/sda, /dev/sdb,/dev/sdc. Those are the drives. You can only mount /dev/sda1, dev/sda2,/dev/sdb1, /dev/sdb2, etc. Those are the partitions.