So when I make a texture I want to put on uke's joints for joint textures, what do I save the file as to put in uke's custom folder?

Take it from someone's properties. Copy and paste the texture in uke's custom folder, good luck.

Click on the right button in the toribash shortcut and choose open file location or C:/Games/Toribash-x.x.
Click Custom -> uke and Copy someone textures to uke folder.
(Recommendation: make the textures by yourself, Save it as targa or .TGA). Done

http://forum.toribash.com/showthread.php?t=108126