To get to Ancud on Chiloé Island, you can take a flight from Santiago to Puerto Montt, and then a bus from the Puerto Montt bus terminal to Ancud.
There are also direct buses from Santiago to Ancud, although the trip is longer.
Another option is to take a ferry from Puerto Montt to Chacao, and then a bus from Chacao to Ancud.
From the city of Castro in Chiloé, there are regular buses that arrive in Ancud.
See more about how to get to Ancud - Isla de Chiloé
See also information on Puerto Montt.