Defragmentation is the process of sorting files that have been scattered all over your disk and arranging them in an orderly manner. Hope you get my definition?

You don't :-|?

Read it again ;-)

To defragment your disk, follow the simple steps outlined below.

1) From your Start menu, go to Control panel.

2) At the top right corner, on the same line with adjust your computer's settings, you'd see View by:, make sure to select category.

3) Click on System and Security.

4) Next, Click on Defragment Your Hard Drive. It's usually below Administrative tool.
If nothing happens, look for and  a program in your task bar with the name, disk defragmenter.

Alternatively, goto Computer from a your Start menu. Right click on one if the Disk drives, select properties. A dialogue box pops up! Now select the Tools tab at the top of the dialogue box.
Select Defragment now.

5) Okay hold on... Before you get all jumpy, Select the disk you want to defragment, say Disk (C.

6) Click on Analyze Disk.

7)Wait for the analysis to be complete. You should now see what percentage of the disk is fragmented. You can now chose whether or not to run defragmentation. I for one usually run defragmentation once 10% of my disk is defragmented.

Once you've made your choice to defragment, click on Defragment Disk.
It should start defragmentation. For best results, you should run your defragmentation when you are sure you don't need to use the computer urgently. If however you start defragment in and then you see the need to use the computer, you can stop the defragmentation by clicking on Stop operation.

You can also schedule defragmentation to run whenever you want it to run. To do schedule defragmentation, simply:

1) Click on Configure Schedule still on the Disk defragmenter interface.
2) Set the frequency of schedule e.g, Monthly,
3) Day of Schedule e.g, 24
4) Time of schedule e.g 7:00pm
5) Select Disks to defragment by clicking Select Disks.... Tick as many disks you want or better still, thick (Select all disks)

That's it! Now you've known how to run defragmentation on your computer and I believe you've scheduled defragmentation too.
You should start experiencing a difference in your computer'computer's speed.

If you experience any difficulties please let me know and I'll reply you as soon as possible.
Source: DaeChuzzy