In the early days of the internet, if you wanted to run an online service you had to buy or rent a server computer, manually install the server software for the service you wanted (often using a very unfriendly text-based interface), set it up, keep it up to date, fix any problems, watch out for security breaches etc.
This was okay if you were a computer enthusiast or a professional, but not so great for the rest of us.
Nowadays, you can just use a managed hosting company instead. They do all the technical stuff for you behind the scenes including installing, maintaining and hosting your service, while you do the actual running of the service. Managed hosting providers are like the engineering department of a ship, while you are the captain and owner on the bridge.
Because managed hosting involves labour, electricity, equipment maintenance etc, you do have to pay for it. However, it’s cheaper than you think: a social network or personal cloud start from around 6 euros a month in managed hosting.
You can find links to managed hosting providers on the Grow your own social network and Grow your own online cloud pages.