And how do I get them on certain creatures?

Tokens are applied to a random creature when you buy/apply them. When a token is applied to a creature, you'll be able to find information on what that tokens does on that particular creature's page. A slightly more sneaky way to find token information is to fight someone else who's got a tokened creature in their ritual and read the "tokens" tab of the fight log.

If you want a specific token on a specific creature, there are a couple ways to go about it. You could always ask around and see if any other players have that creature with that token. Alternatively, you could get that specific creature with more tokens than the one you want, and use Token Removal Gel to remove the tokens you don't want.