Complex sentence: There he joined Jerónimo de la Serna and both moved to Quilca, they planned to take hold of the two ships that Pizarro had purchased to for transportation of artillery and use them to support their operations.
Split into simpler sentences: There he joined Jerónimo de la Serna and both moved to Quilca. They planned to seize the two ships that Pizarro had purchased to transport artillery and use them to support their operations.