First we start by talking about what is the need for doing partition for a hard disk.With out saying the advantages of having different partitions in your hard disk i will say the disadvantages of having only one partition.Every one saves a lot of important stuff and will also be very careful while surfing internet but in these days it is very easy to get attacked by a virus.So if there is no chance of preventing it, we keep the important stuff away from viruses.i mean if we partition hard disk in such a way that the OS files are kept in a different partition from the important files which we want to store.A virus can be removed if it doesn't attack our OS files some how by deleting the file it attacks or by scanning it using online antivirus softwares or by any wares offline but removing a virus which attacks our system files cannot be removed because we cant delete our system files if we do so it becomes the situation of cutting the branch on which we are sitting so we cant do that.So i recommend you to partition your hard drive so that if virus attacks your system or any other thing happens to your OS your directly format your OS which is in a specific partition by getting no effect to any of your data.I think its enough and i might have bored you.Here is the way to format your harddrive in windows.
While partitioning you may increase your partition size or decrease it.First i will tell you how to decrease i.e. shrink the volume and then i about extending it.
Right click on the My computer icon and click on Manage option and wait until a window opens showing you disk management option in the sidepane it will look like this.Click on the disk management option .
If your hard disk has no partitions i mean if your hard drive is totally represented as a disk then you should partition it for sure.After opening it you can see the your harddisk capacity .right click on it and you will find the option shrink volume.
Click on it a window opens showing two text fields which shows you the sizes of the drive after and before formatting.You can comfortably change the partition sizes which you want and then click on next and have a name for the partition and press finish.
After this you will get unallocated space of size specified by you then right click on the unallocated space and click on the new simple volume option and click next next finish.This is how you can shrink your harddrive into partitions.
Now if you want to extend existing partitions you have to first delete the unwanted partition by right clicking on the partition and choosing the option delete volume and now you will get unallocated space with which you can extend the partition which is on either sides of it and you can extend the partition some where else with this space.
Right click on the partition to which you want to add this unallocated new space and choose the extend volume option and add the volume to the right pane if you have 2 volumes or otherwise it the space goes into right column by default .
Now click on next as you did previously and your existing partition is now extended.
And there are many other partition managers with which you can have better experience in partitioning your hard drive.You can EPM Easeaus Partition manager i have tried it,it works fine..