ARTPGs are an elaborate system of tricking other artists into drawing your OCs in exchange for a 200-character block of text.
Basically the way a lot of ARTPGs work is that the characters are initially "born" as a text description. The idea is that this text tells you what the character does/doesn't look like to an extent, and then you follow the game's rules/guides to actually draw the official reference. Something like, the text might say the character is Striped, and then the game rules say stripes can be whatever color you want so you make them pink stripes when you draw the character's ref. Sure, logical enough, good way compromise to make it a game (instead of freeform making whatever you want) but still provide options & variety so not every Striped character looks the same. Critically, this also lets you generate new characters faster than you can draw them, which would otherwise be a nightmare bottleneck for games with more than two dozen players.
But– petsite players will barely even need this explained– all the games have artificial scarcity involved in character features. Maybe they can only be blue if you make them during an event in August. Maybe Striped characters are common but Spotted characters are rare for breeding purposes, so more Striped characters are born than Spotted ones. Maybe there's a new release everyone's going bonkers over!
And on top of this, many players think half the fun is designing the character....
So the end result is that if you get a nascent new character's text string and it's got all kinds of highly-desired features, you can trade or sell it to another player. For a pile of cash. While it's still just a text string.