Board Thread:General Mod Discussion/@comment-32938841-20170828193458/@comment-25330335-20170828201721

Do you mean textures or models (They are two different things)? To create textures, use an image editing program like GIMP or Photoshop, and just create images with the correct size (16px square for items).

For models, I don't really know. To create a model for say, an NPC, you have to build it in something like Blender and then export to native java code.