Go to the windows start menu, if you ARE windows (if not, I don't know what to tell ya), and search "Allow a Program".
Click on "Allow a Program Through Windows Firewall".
Click "Change Settings".
You may need to expand the window for the next part.
Click "Allow Another Program".
Find "Blockland" and add it. If it does not show, I think there is a button to add another program, so just locate your Blockland.exe. My firewall crashes if I do it, so I don't really know.