Ghost is Open Source, meaning the code is free to download and edit. However, as you'll visit ghost.org you'll notice quite expensive subscription plans. There are two options. You either let Ghost (Pro) do all the work for you — they will install, manage and run Ghost for you — or you run Ghost on your own server, and manage and install everything yourself. The first option requires a $25/month subscription plan while the second option can run you about $5/month on Digital Ocean. Obviously, if you know a bit about VPS management, you can find cheaper alternatives to host.

To install Ghost, I refer you to their site: https://ghost.org/docs/install/.