You mean Dedicated? If you use the same computer you host on it is better to host through your Blockland client, but I'll tell you anyway.
Start your Dedicated server by going in your Blockland folder and double-clicking dedicated.bat. After that, start up Blockland, go to join servers, and then query lan. If your server is there, join it.
For some reason I can't join my own dedicated server through query lan, so it doesn't work for everyone.