You can honestly just google "free minecraft server".
Some of them will be scams that need you to go through some survey - which by the way is all fake - but there are a couple that actually give free minecraft hosting.
https://duckduckgo.com/?q=free+minecraft+server&t=ffab

how do i do that?

There are free hosts out there (The name of which I am restricted on saying) but they usually have a catch such as "If player slots aren't full for 15 minutes the server shuts down" or "Server will shut down after 24 hours" or "Make sure to renew every 12 hours to keep the server online!". But like he said, odds are you might be able to just run one yourself.

What kind of system are you running and what kind of internet speeds? You may very well be able to run it yourself no problems depending on what you want to do with it.