I want to learn how to make skins? So if anyone can teach me or do step by step then I would gladly appreciate it :3
I don’t know how, but would love to learn. I want to make my own personal ones and maybe create some to add here as well 
You can check out this handy guide: (2020) The New Guide On How to Install and Make Skins
I’ve looked at that link, but still don’t get it? Thank you though
Skins are located Inside of the game client. If you open Windows’ File Explorer, you can navigate to
C:\Program Files (x86)\Pokemon Mystery Universe, where PMU should be located If you used the Installer.
Further down the directory C:\Program Files (x86)\Pokemon Mystery Universe\Client\Skins Is where you find the Skins folder Itself, which contains your skins and their data. When Installing skins, you put their folder In there.
There should be a folder called “Main Theme”, which Is the default skin PMU uses. If you go Inside that folder, you see even more folders:
They correspond to specific areas In the user Interface, and have Images In them. For example, Main Theme\General\Background has one Image named gui.png, which Is the Image you see In the background of the Main Menu:
If you were to change the Image, It’d subsequently change In game. I did so here for the sake of an example ( never use MS Paint to make skins pls ).
And as you can see, refreshing the skin has applied the change.
Like said In the guide Shrew linked, "all images should be saved in a .png format, and retain the names given to them in the folders (So the reskinned version of “GUI.png” should also be named “GUI.png”". When you edit a certain png In the skin, It should ( aka HAS to ) retain the same file format and name to appear.
By knowing how you find and replace the Images, you can start messing around with help of that guide now, hopefully.