Relevant xkcd

B. oleracea gets all the fame.

B. rapa never gets the respect it should.

https://en.m.wikipedia.org/wiki/Brassica_rapa

Bok Choi

Bomdong

Choy sum

Komatsuna

Mizuna

Napa Cabbage

Rapini

Tatsoi

Turnip

Yellow Sarson

Oil seed Mustard

It tastes like broccoli stems. Some are more tender than others (just like with broccoli stems).

I usually slice into little julienned pieces and marinate it in salt and acid for it to wilt into some kind of modified cole slaw.

You can eat it cooked or raw, I personally prefer raw as a refreshing sweet snack.

Raw, it's a little spicy, similar to radishes. Boiled, it's very sweet. It can take the place of carrots and turnips in soups.

The simplest preparation that'll give you an idea of how the ingredients tastes on its own: cut into thin slices and boil in water with a bit of salt and msg (I personally like to use chicken stock).

The outer layer is very tough and fibrous, so make sure to get rid of that first. Depending on the quality of the bulb, you might also end up with one that's fibrous throughout. Those are not pleasant to eat, and if you happen to get one of those, I assure you that it's not a typical experience.

It's basically like a milder/sweeter turnip.

Better than Brussels sprouts. Anything is better than that hell.

You eat it with your mouth, someone else will be along to tell you how to cook it

Depends, mustard seeds yes. Mustard sauce also yes.