There's definitely no way to use them wrong! I'm in a ton of CS and I don't think I've ever seen one that says you have to use your OCs in the canon lore and if one exists that has... they're definitely the minoritiy.
That said I personally like keeping to some of the original lore when I use a species, so I'll usually use mine in two ways:
1. I use individual species characters to RP / headcanon with friends sometimes and that's not always with other characters of the same species so in that case I tend to keep as much of the original lore that's directly applicable to my character but discard world lore for whatever I create with my friend
2. I like to make groups of completely in-canon characters in the same species that are used together but have enough of they're own space that I still feel like I'm making something that's mine. For example one of my favorites is a circus group I have, and I get to define everything about how the circus group operates while knowing that they live in the world the CS created.