Its like an address for a website, similar to the one on your home or your phone number. How important is it..Well your can't have a website without one for starters.
when you type in a url it sends it to a server called a domain name server or DNS. this DNS gives you the IP address of the site you wish to go to.
an IP address is the address of a computer on the internet or a network, and you're not connected without one.
an IP address looks like this:
xxx.xxx.xxx.xxx where the x's are the numbers
an 'octel' is a set of numbers separated by dots and does not exceed 255