reading subdirectory files

i need help on the file directory structure.i know the root directory has a fixed no. of entries(32) usually.but i don't know abt a subdirectory.

how shld i read files inside a subdirectory by traversing the root directory?

is there a special starting sector value ,if so how do i decode the sector no. from the cluster number?

I know how to get the LSN from cluster no. of the file.but i don't know how to read a file inside a subdirectory.

i would atleast like to know any website that might help me or any book that would come handy.

please help!