Many times we kill ourselves looking for information on the Internet when in reality we have it available on our computer, although in many cases, we need a translator 
We can find a lot of useful content in the Xfce forum or in PTM Wiki, but if we want to know all the components of Xfce, how they work and some tricks, we open a browser and put:
file:///usr/share/doc/xfce4-utils/html/C/index.html
Of course, everything is in English but it includes images to better understand what is going on.