I promised I would release it for wikia newbies, so here it is!
**EDIT: I ACCIDENTALLY SAID CLIPART INSTEAD OF THUMBNAIL. SORRY! PLEASE REPLACE THAT!**
(Be sure to read the little words on the bottom of the images too!)
Step 1
Click on Images.
See that "Images" button?
Click it!
Step 2
Now click that button to
add an image from your computer/gallery!
Step 3
It will now lead you to this option
Click "Choose File". Choose an image to upload (e.g.: thumbnail screenshot). Press "upload photo".
Step 4
Here I uploaded my image- chips (for exmaple)!
I now added my image!
Step 5
After pressing "upload", my photo is in the Image section!
Step 6
See that long chunk of letters and numbers? That your photo's name! What a long name, chip-chan!
Now copy the file's name.
Step 7
Wooo!
Now you can paste the image file name into "image 1"!
Step 8
Hope that it worked! And if it did, cheer! If not, come to me for help!
Q&A:
Q: Does gifs work?
A: For whatever reason necessary, yes. But if you're trying to just cause up trouble, then a magical fairy named Admin/Moderator-san shall come and eat it along with your account! :O
More Questions will be added if there are down in the comments!