The net is a publicly accessible database, where content can be both hosted and accessed by anyone with connection and a device capable of connecting to it. It is identical in function to any local network, but its cultral importance is due to its astronmicaly large size.
At its core the internet has 1 simple purpose - to provide a near endless database of information on any topic, that anyone can contribute to. However, many would argue that in the modern age we've shifted focus towards interconnectivity; using it as a global communication network, as seen with the rise of scocial media, such as Facebook, Twitter, Reddit and Instagram, taking the concept of old web forums, or message boards, where users where able to disscus niche and/or wierd topics among like minded individuals. These sites would strip away the layer of mystique associated with these boards and present them in a much more consumer friendly mannner, shifting the focus from disscusion to comunication.
As a consumer you're able to gain access to the web via an ISP, such as IINET, Telstra or Aussie Broadband, which will charge you an either monthly or yearly fee to access the internet, through either a wired Ethernet connection or WiFi.
An Intranet is used by large entities to limit what is seen on the web when accessing it through their network. This is most commonly used by schools, to limit students access to procrastination tools as well as adult sites. However, like every security system, it's not without its flaws. By either connecting to a VPN or proxy server the effects of an Intranet can be all but ignored.