To get here by subway you'll need to eventually find your way to the F line in Brooklyn.
In Manhattan the A/C line connects with the F in Brooklyn at Jay St. Burrough Hall, so if you're by the A/C, that's a good train to take because it'll get you through Manhattan making only express stops.
When you get on the F train, it's best to get on at the back of the train.
Once you are in Brooklyn on the F you'll get off at the Ft. Hamilton Parkway stop.
If you were in the back of the train you should be right by the Prospect Ave. Exit.
When you get out on the street you'll notice that Prospect Ave. goes up hill slightly, walk on the right side of the street, up hill and under the overpass (total of around 4 blocks)