how to play multiplayer with friend?

hello i really wanted to play teardown with my friend to show him my own map and play campaign later too. the problem is game is expensive for where i live, and only i have it buyed. my friend is not very able to spend money on things like games.
i tried sharing this game with him by sending him the files zipped but it didnt work the multiplayer. i want to ask here how can i play together and if would it work if i give him my steam to login and we both play on the same steam.
(or i heard you can share games with family but im not sure if it still is in steam because i cannot find it)

(i dont trying to ask for pirating the game i want to play legit with the campaign and no mods)