Complex sentence: Xander meets Buffy Summers (Gellar), the Slayer, on her first day at Sunnydale High, as well as her Watcher Rupert Giles (Anthony Head).
Split into simpler sentences: Xander meets Buffy Summers (Gellar), the Slayer, on her first day at Sunnydale High. The same day, he meets her Watcher Rupert Giles (Anthony Head).