The movie opens with Christoph Waltz, as SS Colonel Hans Landa - aka the "Jew Hunter" - politely grilling a French farmer about the Jewish refugees Landa already knows are hidden under the floor boards. This ends badly for the Jews, although one escapes.
The movie then turns to Lieutenant Aldo Raine (Brad Pitt) recruiting Jewish American soldiers for the Basterds, a guerrilla group that fights behind enemy lines in France. Their aim is to slaughter Germans in vicious and inhumane ways to strike fear into the German soldiers. The Basterds are then shown in action, torturing and killing and laughing.
The last member of the Jewish family under the floor boards is now living in Paris and running a cinema. She becomes unwillingly entangled with a German private and the movie Goebbels made about the private's heroic escapades.
That's the majority of the pieces. The movie is surprisingly long on talk for a Tarantino movie: long periods of people trying to pretend to be German and the tension that generates, partially dissipated by talking for too long. And then a minute of extreme violence.
Watching Tarantino movies always makes me feel dirty - this one isn't as bad as Django Unchained, but having seen "Django" before this, I notice the stylistic cues and ideas he's carried over (and in fact has been carrying with him for years, a burden he cannot put down). In particular the "look what a sleazeball this person is, so we can have a graphic righteous kill later." It's a revenge fantasy film, with anyone in a German uniform automatically being worthy of horrendous torture and slow killing. It ends up amounting to excessively talky torture porn, with top shelf actors. If that's your thing, go to it, but I'm done with Tarantino. (Some day I plan to actually watch "Reservoir Dogs," but every time I watch one of his newer films, that day gets pushed further into the future ...)