Select the Poser figure you want to make into your Goth doll. You can use either the preloaded figures that come with the program, or you can download and install one of the figures like "Victoria 4" or "Michael 4" that you can get at daz3d.com.
Go to daz3d.com and renderosity.com and purchase (or download from the free area) the black clothing, black hair and chains you will need. You may be able to find a complete goth outfit you can download. Once you have the items, click on them to install them to the Poser libraries.
Download from daz3d.com and renderosity.com a Goth-type skin texture to apply to your figure. This texture needs to be pale or pasty white with black lips and black shadows around the eyes. If you cannot find a texture you want to use, you can try with a graphics program like Photoshop to open one of the figure textures and modify it. These textures are found in the Poser/Runtime/Textures folder.
Open Poser. Delete the default figure loaded in the scene. Click on the "Libraries" tab on the right to open the Poser libraries. Browse through the "Figures" library to find the figure you want to use and double-click to load it. Now browse through the "Figures" library to find the Goth clothing and hair items you installed. To add them click on the double-arrow at the bottom of the library panel. Then for each item click on "Figure" in the menu and select "Conform to Figure". Select the main figure in the dialog that opens.
Click on the "Library" tab and browse to the Goth texture you downloaded (or modified). You will find it in the "Pose" library. Double-click to install the texture. You now have a 3D Goth doll.