The usual way to travel from the city to Bondi Beach is a train to Bondi Junction, then bus to Bondi Beach.
Here’s a fun way of getting to Bondi I discovered when I visited Bondi Beach for the annual Sculpture by the Sea. There were so many people trying to board the buses for Bondi Beach from the Bondi Junction Bus/Train Interchange for Bondi Beach, the queue was a mile long. We found a bus heading out to towards North Bondi, jumped on that and walked back to the sculptures. Problem solved.
The best way to get to Bondi Beach is to take the Circular Quay to Watsons Bay ferry. The ferry trip takes 23 minutes across the harbour. Here’s the timetable: https://transportnsw.info/routes/details/sydney-ferries/f9/090f9
On arrival at Watsons Bay, walk up past the Watsons Bay Hotel to the Military Rd Terminus (bus stop), which is a two minutes’ walk. From here take bus number 380 to Bondi Beach, the trip takes about 21 minutes. Here’s the complete timetable for the 380 bus route. The service runs around every 20 minutes, even on the weekends.
As a comparison, the train from Town Hall station to Bondi Junction takes 10 minutes and the bus from Bondi Junction to Bondi Beach takes 12 minutes. So, overall the ferry/bus option only takes another 22 minutes and is certainly a LOT more scenic.