Who does Sideswipe kill in the beginning of movie?

You're likely thinking of the 2007 Transformers movie. In that film, Sideswipe does not kill anyone in the opening scene.

The opening scene features a scene where Sideswipe, along with the other Autobots, is battling Decepticons in the desert. Sideswipe is shown to be very skilled in combat and destroys several Decepticon vehicles, but he doesn't kill any specific characters in the scene.

If you're referring to a different film, please clarify which Transformers movie you're asking about.