Sami, You need to enter Multiplayer and then at the bottom there is a save disket. Click there to continue your map.
Itry, to make a map you can go to single player or multiplayer to make it. (I prefer single player as no trolls will disturb you). In single player, build you map and when you are finished, click on the menu icon and save map. However, to edit the map later you need to do it in multiplayer ONLY. (I DONT KNOW WHEN THE DEV WILL UPDATE THE GAME). Hope that help.