Alright, tutorial time! This isn't a very quick process, but you don't seem to have too many characters so you should be fine!

First you select the character you want to add drawings to / edit their creator thing.

To add images onto your characters, scroll down until you see a button called "Upload image" (https://sta.sh/01s2x8f6lccy) and click it. Then you'll be taken to a page where you can upload images of your characters. (https://sta.sh/0jikuiqeb2p)

To change the creator credit of a character, click ownership. (https://sta.sh/01dhgve06bw3) and scroll down (https://sta.sh/0b1evuwb741) to an area that look like this (https://sta.sh/0gliepy8980) From there you'll be able to check off if the person has a toyhou.se account (where you'll only put their username, not the link) or has a link to a different website (where you'll insert the link)

It's also really handy to make folders so you can organize your characters, and if you have a bunch of closed species characters but don't want to make folders for each and every species, give them tags that say what species they are!

Hope I helped <3