To make an Add On, you must have the following things:
For scripts, be it for weapons, items, etc. (The code that makes it an Add On and makes it do something)
-Notepad (Everyone has it. If you don't get off your 3rd party O.S and get Windows XP).
-Knowledge of scripting (You don't just "learn" it, it takes time and practice.)
-Sense of what the people want or would use (So you don't make stupid pointless Add Ons)
For models (How it'll look like in game)
-A 3D object program, such as Blender or Milkshape (There are tutorials on this in the forums somewhere)
-Knowledge of how to use that program (Don't make a box and call it a vehicle.)
To make a map, you must have the following things...
The only way that I know of to make maps is using the Blockland Terrain Editor.
To make a map (Somewhere you can play in)
-Blockland and the World Editor/Terrain Editor mod
-Good knowledge of making a map (Otherwise your map may end up shameful. If it's your first map, and you KNOW it sucks, then don't release it.)
--To improve your own map, you can use custom textures. Be sure you know how though.