Gateway, first book of the Heechee series by Frederic Pohl as per Looking for sci-fi novel I read about humanity finding alien station on orbit of Earth.
Gateway is a space station built into a hollow asteroid constructed by the Heechee, a long-vanished alien race. Humans have had limited success understanding Heechee technology found there and elsewhere in the solar system. The Gateway Corporation administers the asteroid on behalf of the governments of the United States, the Soviet Union, New People's Asia, the Venusian Confederation, and the United States of Brazil.
There are nearly a thousand small, abandoned starships at Gateway. By extremely dangerous trial and error, humans learn how to operate the ships. The controls for selecting a destination have been identified, but nobody knows where a particular setting will take the ship or how long the trip will last; starvation is a danger. Attempts at reverse engineering to find out how they work have ended only in disaster, as has changing the settings in mid-flight. Most settings lead to useless or lethal places. A few, however, result in the discovery of Heechee artifacts and habitable planets, making the passengers (and the Gateway Corporation) wealthy. The vessels come in three standard sizes, which can hold a maximum of one, three, or five people, filled with equipment and hopefully enough food for the trip. Some "threes" and many "fives" are armored. Each ship includes a lander to visit a planet or other object if one is found.
Found by searching for book series alien space station full of mothballed ships autopilot