If I may introduce, Hypnosis, in it's most basic sense, is the ability to tap into the spectrum of thoughts within a target's mind and hide a few colors or add some of your own. It's a basic and inherit technique, so the effects aren't too magnificent, but they will do the trigger.
With Hypnosis, you can introduce or remove memories, thoughts, ideas, distortions, that your opponent will believe true, DURING the hypnosis. If you introduce something foreign, especially something substantial, the more aware of the targets will realize it afterwards, but you can use it while they don't, while the eye contact maintains. This, of course, is the greatest distinction between normal Sharingan Hypnosis and Shisui's Kotoamatsukami, because then you have a much more powerful and overwhelming hypnosis that latches on even after the procedure.
I'm sorry to disagree with Scorps, but you can indeed control your target's will, and have them do something they wouldn't normally do. But you have to play with their psyche. One example would be making them believe they're dreaming, and then having them fly off a cliff. Would they normally walk of a cliff, no. Can you force them to, no. Can you trick them to, yes.
And I had believe you could actually make them feel sleepy and put them to sleep with hypnosis alone. Scorps, are you sure we can't?
AAAAAND, I have some questions:
1. You can only affect people 1 rank lower than you. As an Official Sage, can I affect Unofficial Sages (which weren't supposed to be a rank in the first place)? And can I affect Grims that aren't Official Sages?
2. What about the Bijuu mind controlling stuff, and the animal mind controlling stuff? Neither Sasuke or Obito used an actual technique, they simple looked at their targets ( 9Tails, Manda, etc) and their minds went blank, allowing them to control them without even retaining eye contact. Should this be made into an actual technique, or can we assume this complete mind control can happen with the base Hypnosis effect, but ONLY on Animals and unattached Bijuu?