CBD, or Cannabidiol, is an active ingredient which is derived from the hemp plant. Unlike its cousin the marijuana plant which contains THC (tetrahydrocannabinol), CBD by itself does not produce a "high" and is used for pain relief.
Yes. Congress passed the Agriculture Improvement Act in 2018 which allowed hemp and CBD to be sold and consumed throughout most of the United States.
There are a variety of ways to take CBD, but the most common ways are smoking (such as using pre-rolls) or consuming (such as a tincture or edible).