Finally

Do some background reading now on variable length subnet mask (VLSM) and classless inter-domain routing (CIDR)

Also look up Request For Comments (RFCs) and understand what they are.

It seems like most networks in the world are using the same addresses! Look up RFC1918 and understand why this is the case.

The recommended text book for this module is Computer Networks, 5th Edition by Tanenbaum. Read the chapter on IPv4 addressing; it is section 5.6 in the 5th edition, but the chapter is similar in the older editions.