I am exited to see where this goes!
You have your friend host the server and then you type in your friend's IP address in and click join. Sorry it's a bit of a rough way of doing it but I don't have money to host dedicated servers.
Thank you for the feedback! unfortunately I wont be continuing working on this game because i have bigger stuff planned. This was my first multiplayer game so the code is super messy and i just wanted to start something new with what I've learned from making scrap Defense. Its crazy how many people actually liked this game though :D thanks!