Yes, "Divide and Conquer" was the first episode of Teen Titans. Interestingly enough, it wasn't the first episode to air. The first episode to air was "Final Exam," because Cartoon Network aired it out of order. "Divide and Conquer" was aired as the third episode in the season, after "Sisters."

The episode you're talking about is actually called "Go!" and was the tenth episode in season five. You're right in that it served as an "origins" story, but as far as chronology with the series goes, it was NOT the first episode by a long shot.

No there is one before where starefighter is hold prisoner on a ship
but escaped and became friends with the others

well yes but relly they met in "go" episode 36