It is very conveniently located if you live in the Taksim area. You can get there by funicular. Otherwise, go back to the hill. You can top up your card account in the machines. You can sail to the other side of the Bosphorus, to the islands. The schedule is on the maps. From the marina, you can take a tram to Sultanahmet, Balat, etc.
Ferries depart from this pier in different directions, we went to the Princes' Islands, the ticket is about 100 lira one way. It will cost the same to return, there are ticket offices on the islands, the ferry may be different. The travel time may also vary depending on the boat. We got there in one direction in 2 hours, and back in 1h 40min.