Getting around Santorini is very easy as the island is small and is covered by one bus network very efficient. You can too rent a car but that already depends on how much money you have gone on vacation with. Buses are an ideal means of transport for Santorini so don't worry that they take you to and from everywhere. The buses are also air-conditioned and in high season a high frequency. Of course, we are in Greece so schedules can change without prior notice and you stay at the stop waiting a little longer than you expected.
There are seven bus lines and tickets cost between € 1 and € 2. When the season is high you do not wait more than half an hour for service and if you go from the port of Athinos to the port of Firo or vice versa, the bus that makes this route is related to the schedule ferries. What you should know is that there are no direct buses between the different parts of the island since all the lines pass through the Fira junction so it is most likely that you will have to change buses in Fira. And is there taxis? Yes, and the good thing is that most speak a little English. There is a minimum fee and then the rest depends on the distance of the destination, the amount of luggage or the time of day.
Although I said that it is not convenient to rent a car if you plan to stay more than a week is an option because you forget about buses and transfers. Finally, all the boats and ferries depart from the port of Fira that go on excursions to see the volcanoes and hot springs. This type of walk cannot be missed.