What is the difference between the IPv6 protocol and teh IPv4 protocol?

IPv4 uses 4 octets of data and so represents addresses using number 0 to 255 (2^8). it also uses a subnet mask of similar structure to help define which part of the address is the network address and which part is the host address

E.g.

Address 192.168.0.3
Net mask: 255.255.255.0

In this common example the first 3 octets are the network and the last one is the network, meaning:
192.168.0.0 is the network address
192.168.0.255 is the broadcast address
There are 253 possible clients connecting to this subnet

You can use morerestrictive IPv4 addresses to get different network shapes

E.g.

192.168.0.3
255.255.255.253

Gives:
192.168.0.0, 192.168.0.5, 192.168.0.10 and so on as network addresses
192.168.0.4, 192.168.0.9, 192.168.0.14 and so on as broadcast addresses
With 3 possible clients in each subnet

This is all well and good but unfortunately we are in fact running out of addresses and ways to carve up networks to maximist the utilisation of available IPs what with mobile phones, GPRS, even some fridges have web connectivity and need an IP address.

This is being solved by the invention of IPv6 which uses a 128bit address. This new address space thus supports 2^128 (about 3.4×1038) addresses

This allows for every man woman and child on the planet to have a few hundred thousand addresses EACH. They are also routable and look like this:

E.g.

2001:0db8:85a3:0000:0000:8a2e:0370:7334

To improve efficientcy they can be shortened if lots of duplicate numbers exist in the address but in short IPv6 is the future of IP based networking. Some providers and home routers can encapsulate IPv4 frames in an IPv6 packet which can then traverse the web ver the new technology

For more in depth analysis:
http://en.wikipedia.org/wiki/IPv6
http://en.wikipedia.org/wiki/IPv4

IPv6 is better but most of the internet has to channel these through IPv4 networks. We need everyone to simultaneous jump to IPv6 but it's unlikely to happen that way. i guess having both helps us all migrate slowly.