You don't unarchive the ZIP files, you save them in your addons folder, do NOT save your addons in a zip.
1. Download your addons from the forums.
2. Save them to your blockland directory (usually C:/Program Files/Blockland). NOTE:DO NOT UNARCHIVE THE ZIP FILES.
3. Start up the game.
4. Enable the addons in-game in the addons menu in "start a game" by clicking them, making a checkmark in the box on the right side.
5. Profit