Minecraft – My friends can’t connect to the Minecraft Server

Well, if you are not using LAN than you need to port forward your IP. It is different depending on your router but I would suggest looking up a port forwarding tutorial. You just need to make sure that you use the correct IP when doing this. Once you have port forwarded you should be able to give your friends your public IP address. To figure this out just type in "my ip" in Google. Your friends should be able to connect once you do this.

Opening Minecraft to LAN does not use the port 25565; instead it uses a different port each time. You can use

sudo ufw allow <port>

to open the port and change <port> with the port that Minecraft chose when opening to LAN. Or, if you want convenience, you can allow any connections from your local network here(assuming you trust everyone in your network... which you probably should!)

ufw allow from 192.168.0.0/24 to any

Change 192.168.0.0/24 to the IP range for your network.

Source: Ubuntu UFW Community Help Wiki specifically:

Allow by Subnet

You may use a net mask :

sudo ufw allow from 192.168.1.0/24 Allow by specific port and IP address

sudo ufw allow from to port example: allow IP address 192.168.0.4 access to port 22 for all protocols

sudo ufw allow from 192.168.0.4 to any port 22