A branched scene is where the dvd will play the main feature or episode, and then skip to a different part of the disc to insert a deleted scene, and then skip back to resume the main feature.
I much prefer "seamless branching" which is where you select to watch an extended version, and it will skip back and forth for you, without you even noticing (if it's done well).
If it doesn't say seamless branching, it's usually manual, which has you looking for a logo to appear on-screen, and then hitting the enter button to insert the scene (X-Files, 24 Season 2, X-Men...).
24 Season 3 will probably be manual like season 2.