Do I have to play any Assassin's Creed games (1, 2, brotherhood, revelations) to understand Assassins Creed 3?

you most certainly have to play ac2, ac brotherhood and ac revelations before you get ac3 to get the story

You have to play the 1st and 2nd for sure. If you can, play Brotherhood and Revelations too. But at least play the first two so you can get somewhat of a handle on the plot and controls.

yes of course

It's a good idea to play the first four because the stories are very good and really involved in regards to the amount of depth they go into but Ubisoft has started every single AC game after AC1 by recapping the entire series up to that point. The introductory segments are by no means an exhaustive summarization of all events, but they always do a good job of touching base on all the major plot points. The only thing you're really missing is that feeling of personal connection you get with all the characters from playing the games in their original entirety. If you don't want to play the games, you can always read the stories you're missing from the Assassin's Creed wiki, they do an excellent job summarizing the games and they give a ton of detail—it's the next best thing to playing all the games.