How to create a server in minecraft without buying the game?

Actually, there's no way to. You have to own the game in order to be able to make a server for it.

You can download the server software from here: https://minecraft.net/...t/download

This includes the server, which can be downloaded separate from the client.

Though, without a client and a valid account, you won't be able to use the server, but you can still set one up.

Um. Buy the game, dude. That's like asking "How do I parallell park if I don't have a car?"