Okay first, do you have winrar? If you do not have winnrar it is impossible. Second right click on the add-on you want to put in the game. Click extract
A whole list should pop up, form there type C:Program Files/Blockland/add-ons
and click okay. Then once in-game when starting a server go to the add-ons list and enable the unchecked box in the list. Then start a server, spawn the weapon and or vechcle, and enjoy.