You can get rhubarb seeds, although not much choice of variety (not that there's THAT much difference among rhubarb varieties, IMO). It will be at least 3 yrs before you get a harvesting-size plant from seed.
Most people either buy bareroot or potted plants, or get divisions from friends/relatives/neighbors who are dividing their own rhubarb. Division is usually done in spring just as the first leaves are starting to show; potted plants can be put in anytime during the growing season.
It grows very well in cold-winter areas, not so well in the South where there is no winter to speak of.
Pat