The current internet is centralized, based on the client/server model where billions of us internet users access millions of web sites.
Most of the answers talk in general and do not actually tell how can a computer be made to act as a server.
This is very important step if we want to actually decentralize Internet.
Please refer to 2 tutorial pages from our ‘Decentralized web’ project -
dWeb tutorial - outward and inward communication
dWeb tutorial: Enabling inward communication