You just do stuff. Like, you say you want to join, and in some simulators, you make your characters. In others, they get made for you. Then, you can quote options once the creator of the sim mentions you in it.
Melon and Panda Child please? Panda Child has one Digger Paw, one Runners Leg, Short Snout, Ram Horns, a brown mane, blue eyes, a brown Horns, and a black panda pattern he was made in the early days of Niche.