Ama-network analysis

Hi friends my doubt is related to Q.T. topic critical path analysis - i can very well correctly solve problems but mechanically. I mean to say that i can calculate est,eft,lst,lft;FF&IF but i am unable to understand their relevance what does these represent and how are they actually helpful PLEASE ANS. i have no friends or teachers to help me. BUT YES I HAVE UNDERSTOOD RELEVANCE OF TOTAL FLOAT ONLY coz that is clearly given in book