like celery. cut off bottom part that was in/near ground and cut off leaves, chop stalk
if it's very stringy, you can string it like you might celery. but this often takes away some of the red color, so I try not to do this. it will all soften when cooked, and you do have to cook it with some sugar or it's too tart. but as Marg mentioned, we took raw rhubarb and dipped it in sugar and ate it that way as kids. I would no longer do this to myself.