How do I use set spawn or whatever it is called

In the .minecraft/config folder, there should be a file called something like "setspawn.json". It is already configured for many different seeds, but if you want to add a new seed then simply copy a configuration and paste it at the end, then change the seed and coordinates. Or another option is to change the parameters of a seed that you know you will never use.

i do not have a .minecraft/config folder.

/setspawn

and then how do i make the world spawn the same every world? do i just use recreate?