This belongs in the help section.
Ok I have a mac so I believe I can help you ha. First off how you find your addons folder is through finder. Follow these step by step instructions to find your addons folder:
1. Click Finder. (The Smiley blue character guy on your dock to the very far left)
2. Click "Applications" on the left side of the Finder Window.
3. Scroll down until you see a folder that is named, "Blockland v10" and open that file.
4. Inside you should see a file named, "Add-ons". If you do not see this, please re-install Blockland.
This is your addons folder, any file you download you put into this folder. (.zip and all)
I recommending downloading the RTB addon first. Partly because it makes downloading addons a lot easier, because it has an ingame downloader where you click an addon and download it strait to your file without click and dragging files.
Hope this helped. Also please for future notice, read the forum rules and post in the correct section.