Hello, bluejay, and welcome to Roleplayer Guild!

Usually, one posts CSes on OOC threads. The Game Master (GM) will usually post your PMed CSes on the OOC for other players' reference and comfort.

As for original artwork for character appearances, one usually posts it along with their CS in the OOC. Whether original artwork is allowed at all depends on the GM.

(Don't worry. I'm a GM myself, and I would be impressed if you did original artwork. But sometimes, some GMs require you to add in some text with your artwork to settle differences between the artwork and the envisioned character e.g height and weight. Or for the really advanced GMs, they might encourage text over pictures. This site does encourage creative writing, after all.)