Maragas (Marangas) is actually the north end of Plaka beach. It is right after Agia Anna and you will immediately notice when you have reached it - as soon as you see tables of a taverna under a big tree with twisted branches.
Maragas is calmer because it is a bit away from the beach bars and there are rocks on the sea bottom. Like the rest part of Plaka, it has coarse sand and blue water. The far end is often occupied by nudes - this is the area around the rocky peninsula which separates Maragas from Agia Anna.