Friendica is a truly decentralised social network, it has been around for a few years now already. Back in the day it was called Mistpark and already then it was more than just a proof of concept.
Today Friendica 3.0 is released and it is now ready for even more users than ever. Friendica is easy to install, it's Php and Mysql based, so it can even run on a shared hosting platform. There are many plugins and some of those plugins are connectors that can allow you to connect to legacy social networks suck as Facebook and Twitter, but also StatusNet and Diaspora.
Friendica is exactly what many of us have wanted, and these guys, mostly Mike have worked hard and have delivered harder. The project deserves that you try it out. So go install it, or try out a test account on a test server to see what it's like... If you really don't know have a clue about installing "websites" or anything, register an account with a public server.