Making an online server

Before I say anything, I have read other Posts and none give me the answer i need.

Right, anyway me and a friend are trying to make an online server but all that comes up when he or me tries to join each others servers is THIS SERVER IS NOT RESPONDING.

Possible solutions as to how i could fix this?

Have you forwarded your ports? Is your firewall off?

Windows defender up?

I have EXACTLY the same problem so i second Kitty’s post.