SkinMagicBuilder is a tool for creating new skins or editing existing ones.
Skins are stored in files with extension *.smf.
Brand Builder Tool is shipped with a number of prepared skins, which you can use for creating private branded softphone version.
Also, you can create totally unique design of softphone. For these purposes you need to use SkinMagicBuilder tool (see below screenshot).
You can start creating skin from the scratch (from empty *.smf file), but this is not recommeded. The skin file contains a skinning for many elements, like buttons, text edit controls, sliders, scroll bars etc. It is easier to take an existing skin file and make necessary changes to it. Most of elements are not necessary to change and you can leave them untouched as in an original file.