<p>I am reading about COFF file formats, which is commonly used to create an executable file format (it has some variants also). </p>

<p>While reading, I came across the relocation section of the format. How is this relocation section used to create an executable file.</p>

<p>It would be very useful if you point me to some links which will help me.</p>

Relocation is used to place executable code in its own memory space in a process.  For example, if you try to load two dlls that both request the same base address (ie, the same place in memory), then one of the dlls will have to be relocated to another address.
NTCore
is a useful site for exploring Portable Executable (PE) files, which is what COFF is now called.
Here
is another site that explains relocation pretty well.