Complex sentence: Narendra Nayak started working as lab technician in the Kasturba Medical College in Mangalore and was an assistant professor of biochemisty when he took voluntary retirement in 2006, after about 3 decades, to work full-time in the rationalist movement.
Split into simpler sentences: Narendra Nayak started out working as lab technician in the Kasturba Medical College in Mangalore. He was an assistant professor of biochemisty when he took voluntary retirement in 2006, after working there about 3 decades, to work full-time in the rationalist movement.