Complex sentence: In 1580 his first expedition with Juan de Garay he served as Captain, attended the foundation of Buenos Aires, and where accompanying him on dangerous missions, where aboriginal natives and exotic animals were the main obstacle.
Split into simpler sentences: In 1580 his first expedition with Juan de Garay he served as Captain, attended the foundation of Buenos Aires. He accompanied Garay in dangerous missions, where aboriginal natives and exotic animals were the main obstacle.