LinuxTent

When you want to format a certain partition, first you need to know the label of the partition (for more information about this go here)

To that enter this command in your terminal,
df
under “Filesystem” you will find the label you want, and under “Mounted on” you will find the mounting point.
Now to format it you have to unmount it first :

sudo umount "Mount Point"

Then you can format it, there are different commands for formatting depending on which filesystem (FAT, Ext2,Ext3, Ext4, … etc) , for example lets say i want to format my flash memory stick which is under the filesystem label /dev/sdb1 , it is mounted on /media/disk, and I want to format it ext2 i will do this

sudo umount /media/disk
sudo mkfs.ext2 /dev/sdb1

ENJOY!