Arma 3 multiplayer mission

I try to do an online mission and play it with my friends. But when I
click on the new host and make it my friend cant find the server server ... Is
grateful for all the answers!
(I think it depends on the gate to open, but if so, how do I open the gate)

- Checks when you create the server if you put "Internet" and not "Lan".

- Try to connect in direct IP address, with the IP address and the gate.

- Ask to your friends to create a server and look if you can connect on it.

Tell me more when you did it.