Complex sentence: After rescuing Magneto from the zombies which attacked and killed his teammates, Red Skull takes him to his secret hideout and tells him about his plan to destroy the Shield using his powers over magnetism.
Split into simpler sentences: After rescuing Magneto from the zombies which attacked and killed his teammates, Red Skull takes him to his secret hideout. He tells Magneto of his plan to destroy the Shield using Magneto's powers over magnetism.