Locating the default graphic files
Like with the font settings (and everything else) the skin graphics work on a hierarchy system which means you only need to copy over files you are planning on editing into your skin, if you don't copy the files over the game will just use the default files.
The first thing you need to do is locate where in the 'Working' Folder the default skin graphics are located, and like with the text settings they are located in various places, however instead of being located inside the settings folder the graphics are aptly located inside the graphics folder.
The first location you need to check are the folders for the parent skin to your skin (when skinning this should always be the first place you look for files), if you cannot remember which parent skin you set then open the 'skin_config.xml' file located within the 'my_first_skin' folder and locate the parent line that looks like this:
<flags id="parent" value="fm dark-widgets" />
In this case the parent skin we need to look in is 'fm dark-widgets'.
So in your Working folder browse to the 'skins\fm dark-widgets'folder, but notice that there is no graphics folder for this skin, that is because this skin has no unique graphics and inherits from its parent skin.
Now what you need to do is locate the parent skin for the 'fm dark-widgets' skin and check if the parent skin has a graphics folder.
The parent skin to the 'fm dark-widgets' skin is the 'fm' skin and whilst this skin has a graphics folder it is empty apart from a config file, so you now need to look in that skins parent skin.
Now you should be in the 'skins\fm-widgets\graphics' folder and notice a load of folders these folders contain the skin graphics for full mode skins. This folder is where you will be taking most of your skin graphics from.
Graphics are also located in the 'graphics' folder located in the root of your Working folder; this location contains the general game graphics (logos, kits, pitch graphics etc…) but you shouldn't really need to touch these for basic skins, you might touch the main menu folder if you want to change the title screen but that is about it for a skin.