To make a decal available to the public, do one of the following:
a) use the "attach" function here on the forums (when you make a post)
b) upload the pic's to an image host, use the linky's to post 'em
c) pack 'em in a .zip, upload it somewhere (Mediafire, for example) and post that link.
Making new maps is done with some of the following:
Torque Constructor (for interiors, a big part of map making)
QuArK (same as above, just a different tool for it)
the Blockland Mission Editor (making terrain, placing interiors and shiz)
Add-Ons are made with some kind of text editor like Notepad.
It's just scripting in TorqueScript.
Models (for the addons) are made in MilkShape, Blender, and various other things that I don't remember.
Add-Ons can be found
HERE.
(It's the Add-Ons board lawl)
