Don't expect a fantastic uptick in visual quality -- those ray tracing effects just use to shadows, so you are simply going to find a softer, more realistic regions of darkness when you are making use of the choice.
You'll need a GPU that supports ray tracing tier 1.1, with the latest drivers, in addition to the May 2020 update for Windows 10 -- and, clearly, you'll need to be using DirectX 12.
You can head to the Blizzard site to opt-in to get a chance at beta accessibility, too.
The people at Wowhead have caught a load of comparison shots to show what those ray-traced shadows look like. It is a pity WoW ray tracing will not go beyond shadows for today, since the stylised design and easy character models would appear incredible under the spotlight of extremely realistic lighting.