OS X Mavericks :: Listing And Closing Open TCP Ports?

For security reasons I would like to have as few open TCP ports as possible on my iMac, leaving open only those that I feel are worthwhile having enabled. How can I go about to 

a) identify which TCP ports are currently open on the system

b) identify the processes that have opened the ports and understand the origin and purpose of those process

c) disable the processes that have ports open, if I feel that there is no good reason for having them open 

I'm running OS X 10.9.4. 

Info:
iMac (27-inch, Late 2013), OS X Mavericks (10.9.1)