Hi Vaibhav,
To add to what has already been said so far...
The get_related_entity( ) method basically gives back a BOL entity related to the BOL entity from which it is called. And depending on whether the relation is 1:1 or 1:N, the method either returns the related entity itself (1:1) or returns the first related entity (1:N). For example: If objects A and B are related to each other by relation C such that A is higher in the model, then you will get instance of object B when you call get_related_entity( ) method on object A and pass relation name C to it.
Regards,
Shiromani