I use a Dell Studio 1555 laptop and I want to install Ubuntu 12.04 on it.
I want to know if I can create a partition on my hard disk after installing Ubuntu on it.
I want to create partition as we do it in Windows like
E: drives etc.
Based on your comments above you have a primary partition (sda1), an extended partition (sda2) and within the extended partition you have a logical partition (sda5-swap).
It is not clear if you want to make a primary or a logical partition. In either case, you will need to shrink the sda1 first to free up some space.
In gparted you can click on the sda1 partition and drag it's right edge to shrink it.
Once you have some unused space, you create more partitions.
To create a logical partition you have to shrink sda1, expand the extended sda2 to cover the newly created unused space, and create new sda6 logical partition inside sda2.
You can try this in gparted, nothing will be done until you click Apply.
yes you can do it , there is a tool named as gparted . you can get it by
sudo apt-get install gparted
after that type as gaprted in unity dash and that will list you gaprted app . click it to open . select the empty with right click and choose New . then from that you can choose what kind of partition you want and how much size you want to give for it .
and moreover you can do it from a LIVE CD/USB Session also if you're installing Ubuntu from a live session .
Hope that helps .