How to make a server?

You will have to start off with steamcmd, from there locate the server id of any game that doesnt require a purchased copy. I recommend that you read up on steamcmd commands as well as the game you are interested in making a server for.
Not to mention will your internet or hardware support said computer.
If not then you will need a virtual private server or dedicated machine, VPS is the cheapest route where as I pay 124$? For a dedicated machine.