When the meat goes into the bag, does that end up in the oven? (I have a very very basic set of cooking skills, so this is a serious question.) Thanks.
No, the temperature of the water cooks it in the bag. If you want it browned that can be done with seasonings in the bag or it can be browned superficially in other ways, like on a grill as I’ve done, in an oven or with a specialized gas browning torch like some chefs use.
You don’t need to buy one of the expensive dedicated sous-vide cookers either, there are fairly inexpensive devices that circulate the water in your sink and keep the temperature at a consistent level, that’s what I use. Tons of videos on YouTube, go have a look.