Do you sous vide and how hard is it?

I just bought a food sealer and thought I'd use it for sous vide. If any of you cook this way, could you please tell me if it's as tricky as all my research says it is? Is it really a precise method? Is it dangerous in regard to possible bacteria contamination and production? It would be nice to just heat up a big pot of water to boiling, then turn temp down to simmer and cook the bag for a decent amount of time. Why does all my research make it seem like a "science"? Haha!
Edit: OK!! Now I get it!! It's all about temp : time! In hindsight, I shouldve figured this out. Was thinking more like a crockpot.....cant really ruin anything with a crockpot!! (Maybe I just know how to use it after all these years). Anyway, thank you EVERYONE for your help. I appreciete all your comments, except the one from that grumpy person.