How do I unlock the Minecraft port on my Speedport Smart 3?

I want to host a local Minecraft server and have to activate the TCP and UDP ports so that my friends can join. However, this does not work, although I have done it as it is on several forums.

I don't know the router's interface, but it seems like you're on the right track.

You have assigned a name and selected the corresponding device. You now only have to enter port 25565 everywhere in tcp, then click on save and wait a moment. If it is still not accessible from the Internet after 5 minutes, you can try restarting the router.