To start a dedicated server please make sure you can host in the first place by checking your ports to see if the game is forwarded and that no firewalls are blocking it.
Go into the main directory you placed the Blockland folder and open it. You should see a file along the lines of "dedicated.bat". To change the map right click on dedicated.bat and click edit. Change the map from Bedroom (Default) to something else. To configure the game settings go into base\config\server. Click on Prefs.cs and open it in Notepad. Change the settings and save. Go back to dedicated.bat and click on it. The window that opens will ask for your Blockland key if it is the first time you have opened dedicated.bat. Enter the key and the server should start.
I hope this helps you