How create own server

Can I create my own server from scratch without paid hosting?

a Python flask server is easy to set up and free, just look up how on youtube

Yes, you can do it from your computer and your internet provider. There are tutorials on YouTube, I did a tutorial some years back on how to do with as well. Best of luck

You can host it from your own computer, but many problems arise from doing so.
First of all, your pc will run hot unless you have a good water cooling system. Secondly, unless you have some godly ISP package, everyone will suffer from incredibly bad lag, including the people in your household. And thirdly, if you plan on having a public server long term, you might as well save yourself some money and simply buy server hosting.
This Video seems to explain setting up your local server quite well. But, iirc you will need to port forward the server to have other people connect to it via the server browser. That step I cannot help you with as I simply don't know.

Edit: I should probably leave you with some more information. This YouTube playlist will help you setup some of the basic's after you get your server in a functional state. This YouTube playlist will help you setup things like custom huds and money printers. And this YouTube playlist will guide you through even more things. The YouTube channel that this content comes from was very useful for me when I decided I wanted to run my own server.