YouTube super chats are just basically a one-time donation that YouTube/Google takes an automatic 30% cut from, in exchange for displaying a message the donor submits along with the payment, pinned to the top of the stream's chat for varying amounts of time (more money donated = longer time pinned/longer message length allowed).

The Bits thing on Twitch is more or less the same thing just without having the message feature necessarily tied to it, users can choose to use the "bits" in whatever way they want to, such as highlighting messages in chat or redeeming certain pre-set features determined by the streamers themselves, they wind up just showing up on the backend as income for the streamer the same as anything else. This is why it's preferable for most people who are using these platforms to simply go with a third party donation service like Streamlabs' payment processor or others who take a far smaller cut, though this proves to be too much to ask of most viewers (unfortunately).