Think of it like an address on an office building. The post office delivers all of the mail to 123 Candy Cane Lane. The name on the letter doesn’t matter to the mailman, they have no clue where Fred Smith’s office is located, and they aren’t allowed in the building anyway even if they did. The receptionist at the office takes all of the mail and passes it along to the correct person based on the name. If they’ve been told where Fred Smith’s office is located, they deliver it. If not, they assume Fred Smith doesn’t work there and they either reject it or just throw it in the trash.
Your ISP is the mailman, your gateway/router is the receptionist. The name on the envelope is like the port number. As long as you configured the router to take traffic meant for port 25565 (default for Minecraft server) and forward it to the INTERNAL IP address of your minecraft server, it should work if your friend connects to your PUBLIC IP address.
Depending on your ISP, you could be in a double-NAT situation, which basically means there’s another receptionist in between, and you have no way to tell that receptionist who is who, all they do is reject all mail unless they’re told ahead of time to expect something in return of what you sent out. If that’s the situation you’re in, you won’t be able to run a server at all without a VPN that allows port forwarding, or some other sort of method to proxy the connection.
Think of it like an address on an office building. The post office delivers all of the mail to 123 Candy Cane Lane. The name on the letter doesn’t matter to the mailman, they have no clue where Fred Smith’s office is located, and they aren’t allowed in the building anyway even if they did. The receptionist at the office takes all of the mail and passes it along to the correct person based on the name. If they’ve been told where Fred Smith’s office is located, they deliver it. If not, they assume Fred Smith doesn’t work there and they either reject it or just throw it in the trash.
Your ISP is the mailman, your gateway/router is the receptionist. The name on the envelope is like the port number. As long as you configured the router to take traffic meant for port 25565 (default for Minecraft server) and forward it to the INTERNAL IP address of your minecraft server, it should work if your friend connects to your PUBLIC IP address.
Depending on your ISP, you could be in a double-NAT situation, which basically means there’s another receptionist in between, and you have no way to tell that receptionist who is who, all they do is reject all mail unless they’re told ahead of time to expect something in return of what you sent out. If that’s the situation you’re in, you won’t be able to run a server at all without a VPN that allows port forwarding, or some other sort of method to proxy the connection.