Sous Vide is French for "under vacuum" or "under pressure." Food is sealed in airtight plastic bags and cooked in a temperature controlled water bath.
Meats, vegetables, and fruit are perfectly and consistently cooked, every time, to the desired temperature.
They can be held, inside of the Sous Vide water bath, at the exact temperature for literally days.
Therefore, the wonderful thing about it is that you can cook steaks to a specific internal temperature (for example, a perfect medium), and they will remain evenly cooked, at that precise temperature until you are ready to serve them. Then you remove the steaks with all of those amazing steak juices, sea salt, pepper, fresh garlic, sprig of rosemary and butter that have permeated the meat, and just flash sear them on all sides in a pan, quickly basting with butter, to get a beautiful, dark, crispy outside.
To accommodate, differing steak temperatures, you would simply keep the steaks ready at a temperature of rare. Then you would pan sear the steaks, basting with butter, removing each when it is ready. If you are not familiar with the touch method, for determining the doneness, then you would want to use a meat thermometer. (You can also find disposable meat thermometer toothpicks at the grocery store, like these shown below).