[Thak2]

Click on the big add button, then under image type the images name.
Fill out description however you want to.
For sprite index, put a sprite number down that is not being used up, hold your mouse over a sprite to see its index.
x,y,w,h are pretty much the same as setimgpart if you have ever used that command.
x being the x coordinate of the top left part of your wanted image, and y being the y coordinate of it.
w is the width in pixels, and h is the height in pixels.
Then click the add button closest to the top.

Now the image will appear on the side.