Main character Theodore, played by Joaquin Phoenix installs a new operating system on his desktop computer. The O/S has been designed with artificial intelligence and takes on a personality. Theodore begins a friendship with the computer voice Samantha, played by Scarlett Johansson which turns into more. Samantha learns the likes and dislikes of Theodore, reminds him of appointments, meeting, important emails, sometimes offers "advice" , and follows Theo around via a portable handheld device which can see and hear what Theo sees. Theo constantly is talking to Samantha throughout the movie via this portable device and an ear bud.
The movie reminds us that we sometimes become too dependent on our personal devices. It is more about relationships than Sci-Fi as you might imagine from the plot.
I would rate it 6 out of 10. There is brief nudity ( not Scarlett ), liberal use of the f word (not in a nasty way), and some strong sexual references. Not a movie you want to see with teenage children or younger.
IMDB trailer and other info: Her (2013) - IMDb