Following the instructions it became clear to me that the type and the version of the server is important. I became to conclusion to get the latest versions of Vanilla and Bukkit. I started with the Vanilla server. It was very important to remember to give the rights to use files and make the start.command file so, that it finds the minecraft_server.jar.
Now it seems that both servers are working fine and i got through to Hullcraft, which was a fine experience.
Here are pictures of my server working.
Among the interesting things I've learned is to change the game mode that is very useful. when the creatures tried to come to my place I changed the mode and took some weapons to fight with.
Nobody has visited my world yet, because it is impossible to keep it up all the time. I was able to connect with one of the students' server and go into his game.
What I learned this week is:
1) How to set up a server.
2) Differences between servers and there setup.
3) Join to a multiplayer world
4) To use console for example to change the game mode.
5) Differences between Minecraft and Minecraft EDU in server set up and use.