Marina was an interpretor for Cortes. She translated from Nahul to Mayan so that a Spanish priest who had learnt some Mayan could translate to Spanish.
Cortes conquered the Aztec empire because the native peoples in Mexico revolted against the Aztecs. So it was far more than 350 Spanish versus the Aztecs by themselves.
Also, he brought with him European illnesses that the Aztecs had no immunity against. It happened to break in the Aztec capital just as Cortes arrived to attack. This allowed him and his native allies to slaughter the Aztecs while they were week from the disease.
Diseases later wiped out most of the native populations.