Appearence and shelf gadgets. (quality of life)

Hello ^-^

Here go my questions:

1. I have downloaded some visual stuff from gnome look (Nordic-dark theme, posy cursor, candy icon) and im not sure on how to apply them to my bodhi.

2. How can i add softwares to the desktop? I have created with Thunar a folder with some photos (i'll talk about it in the next question) and it doesnt appear on the desktop screen. here is the directory /home/computer/Desktop/photos/. I have downloaded firefox via terminology and it doesnt appear on the desktop nor shelf.

3. I want to add a slideshow as my wallpaper (a folder full of images), am i able to do it, if yes how?

4. I am very new to this linux stuff. How can i know my system better. When i try to install things its always confusing bc of all the therminology. I now that bodhi is linux and ubuntu, and i know i have installed the hwe version (bc is the lighter ISO) on the site, but thats it. I know nothing about GDM, Kernell, GTK3, Shell and other stuff

tysm if answer any of that. I did my research here and there but im tired of not finding much clarifying info.