This riser arrives fully assembled, and just sits on top of your existing desk. Put your monitor(s) on the top shelf, your keyboard and mouse on the bottom, and use its integrated spring system to raise the entire setup from a sitting to standing position within seconds. I own a very similar product from Varidesk (which was much more expensive, by the way), and I absolutely love it.
I can tell you from experience that you’ll definitely want a good anti-fatigue mat for standing. This one has great reviews, but whatever you choose, make sure it’s at least 3/4" thick.