Whichever you're using, there is likely a router involved, whether it is your home network or a public network such as at a coffee shop or a business network, or a community wireless network).
If you're not using your own network, you'll need to speak to the person responsible for that network for details on how to fix any issues.
If you have no Internet access a series of troubleshooting steps will help to determine where the breakdown is and how to resolve the problem.
When your Internet service is disrupted, there can be many things that have gone wrong.
The next few sections will expand these steps into a series of instructions.
Where Linux is indicated, I've based these on Linux Mint, the version I'm currently working with. This connects other computers in your network as well as providing access to the Internet via your ISP.
A network is a collection of computers and other devices connected and talking to each other.
Most connections are via a router and provide you with access to any other devices connected to your network as well as to the Internet. If you are using public access from a connection that you don't control (something other than your home network) or one that isn't secured properly (you haven't changed the default passwords or enabled security) then you are placing your computer and data at risk.
If you are setting it up for the first time, the steps listed below were not designed with that purpose in mind.
You need to follow the instructions that came with your router or modem.