Clovelly Beach is a great place to learn snorkeling as it is very well protected from the ocean. This beach is in the South of Sydney between Bronte Beach and Coogee Beach / Gordon's Bay. A very narrow bay goes from Clovelly Beach to the ocean and some large reef protect this bay against the waves and currents. However, because the bay is so well protected, the water is often quite cloudy and if you don't go there on a sunny day you may find it difficult to see the fish and the marine wildlife. If you go snorkeling there you will see the Australian Mado, the Smooth toadfish, many Grey Sweep, and some urchins. If you are lucky you could see the White-ear fish hiding between the rocks.
Compilation of snorkeling videos at Clovelly Beach:
Earth view of Clovelly beach, both sides of this narrow bay are suitable for snorkeling. There is also a swimming rock pool and the rocks on the sides are covered with concrete, with some ladders that allow you to go into the water.
Clovelly beach is a nice place to snorkel if you are a very beginner. Parking can be difficult but a few buses are going there from the center of Sydney: