Angistri has two ports. Skala is where you land if you take the ferry, and Milos. They are only about 15 minutes apart if you are walking, and there is also a regular and large modern air conditioned bus shuttling around the island during tourist season.
The reason for the two ports is that the larger ferry boat needs a deeper platform that can accomodate the arrival of cars and supply trucks in Skala. Most tourists stay there as it has plenty of hotels, many right on the beach.