Dressing Room: Manual (2/3)
Window: Customize Selection | Group: Select Type(1)
First select any type from the DropDown Box(1), after that in Select Parts(3) possible selections appear.

Group: Select or Deselect(2):
Here you might choose wheter you want to use the parts(4) ONLY and ignore all other textures of that texture pack, or whether you want to use ALL textures of the TexturePack EXCEPT of those selected parts! The "Use"-Button(5) changes its caption depending on this selection!

Group: Select Parts
First select some of the parts of the list(3), or select all(4), then click on the "Add selected parts to the list" Button(4) to add them to the Selected Parts list (4).
Group: Selected parts
The list(4) shows the parts you've selected. Now you might either decide to use those parts (or all textures except of those parts, check "Group Select or Deselect"). Click on the "Use"-Button(5) to finish your selection, or "Cancel" to ignore all changes you've just made!