You have to know how to 3D model to create armor meshes - the most common programs used for this are 3ds Max or Blender (the latter is a free application). To create armor meshes you need to get your hands on the originals in editable format, so you can change it while making sure that it will fit, which are in Talad's possession only - so if anyone wants to contribute with this, they really have to apply to the team, which would mean already having a good portfolio to show.
There are a ton of 3D tutorials online, and as for it being easy - it really depends. Some people pick up on it immediately (usually those who already have some art skills) and others may need to really practice day and night before making something really good. There's no harm in trying it out, at least, so give Blender a download, follow some lessons, and see what models you can come up with :} After you're confident in your skills, send in that application.