Use the layers from Plone Default plus your skin folder

The next things that happens is that your should see the following screen with the new skin listed below the other two skins.

The zoom-in of that screen shows your new skin, but with no Layers listed. Select all the layers (there are lots of them so be sure to get the entire list), do a copy (CTRL-C keys), and then paste them (CTYL-V keys) into the empty box next to your skin a_first_skin.

In the new list of layers you just copied, insert the skin folder name into the list below the custom layer name. In your case, insert the text a_first_skin as the second line in the layers list for a_first_skin.

Then click the Save button, to make these layers stay with your skin (see below):

We are almost done. You now have a valid skin folder with layers registered as a skin. However, we could make changes to that skin all day and never see a change to the website. Why? The default skin is normally what is showing and we need to change that next.