How to make the skin of arms and what this program's needs?

Download Slab6 (http://advsys.net/ken/slab6.zip).
Click help to see all the controls. All the skin files are in the kv6 folder inside your Ace of Spades folder. You can edit the kv6 files or create your own with Slab6.

Some basic controls in Slab6:

Movement - W, A, S, D
Click and drag to turn the camera
Ins - Add a block
Del - Delete a block
Home - Add many blocks
End - Delete many blocks
Space - paint blocks
Shift + Space - paint many blocks
Right click - select color

Hope this helps.