How can I link 4 different forms to relate to one form ?

How can I link 4 different forms to relate to one form ?

Hi, I'm entering data about a client and what that client is purchasing through my company. I have divided my information into 4 forms which includes information about my client's details on the first form. Can someone advise me as to how I can easily and quickly relate all these forms as a whole to each client please ???