If I read that correctly, you are trying to mount a non-partition. It could be a simple typo in that you should be using "/dev/sda1" or "/dev/sda2" etc.. instead of just "sda"
If that's not the case, you'll need to use a partitioning tool such as fdisk or gdisk (or a GUI based tool such as gparted) to create a partition table and a partition. Then install a filesystem in that partition using "mkfs".