FYI, the RTB Downloads system works best if on Vista or Windows 7. On XP, which I have a suspicion you are using, is a little harder.
-- Find the download link, follow it.
-- Once you get there it should say "Open or Save"
-- Select save
-- Save to your Add-Ons Folder in your Blockland folder.*
*The Common File Path for the Add-Ons folder is is C://Program Files/Blockland/Add-Ons
However, if you are downloading Add-Ons off the BL Forums, it is a little more complex as there are many download sites that you can download from. The most common is Mediafire.
Either way, follow the same steps as before.
If you are downloading Music, use the same file path, except instead add C://Program Files/Blockland/Add-Ons/Music
For Downloading a .bls file, direct the file path to C://Program Files/Blockland/saves/(map**)
**For map, save the .bls file into the correct map that the file fits in.