Complex sentence: Ternero started his coaching career as assistant to Sergio Markarián at Universitario de Deportes, when Markarián resigned, Ternero was given his first opportunity to work as a club manager.
Split into simpler sentences: Ternero started his coaching career as assistant to Sergio Markarián at Universitario de Deportes. When Markarián resigned, Ternero was given his first opportunity to work as a club manager.