I was diving down in Woods Hole yesterday. I've only done three dives there, so I don't pretend to be an expert, but here are some key factoids.
Garbage Beach is literally just a stone's throw away from Woods Hole Oceanographic Institution and the Martha's Vineyard Ferry terminal. From the Bourne Bridge rotary, take 28 south into Falmouth. In Falmouth, turn right onto Woods Hole Rd. (well-marked). Proceed into Woods Hole past the ferry terminal and across the small metal draw bridge. You will pass WHOI on your left. Shortly after you pass WHOI and just before the NOAA facility you will see Garbage Beach is on your left. If you reach a 90 degree right turn in the road, you've gone too far. Parking is at metered spaces on the right side of the road about 100 feet from the water -- $1.00/hour. Meters are strictly enforced due to abuse by ferry goers.
There is a small stone staircase with a railing from the sidewalk down to the "beach". The beach itself is sandy and there are some small rocks as you enter the water -- nothing too treacherous. If the tide is right, there is a small seawall "seat" near the water line on the left side of the beach that you can sit on to don your fins.
Note that this dive can be somewhat tricky due to the currents in the area. You can easily reach a depth of 50 feet within 100-150 yards of the shore. The key is to keep a careful eye on the currents while you're underwater. When I was there last year, we saw no current whatsoever. On our first dive yesterday, we ran into a pretty stiff current when we got down to about 40 feet -- constant finning without stopping was required just to maintain a slow forward pace. We eventually retreated to shallower water where the current was minor. The Falmouth police stopped by after our dive to offer a friendly "be careful".....apparently at least one diver has died at this site in the past.
2 areas to explore in shallow water at this site -- (1) the WHOI pier that borders the left side of the beach. Great place to explore among the pilings for lovely anemones and other small critters. (2) The NOAA jetty that borders the right side of the beach. Starts out pretty shallow -- lots of large boulders with all kinds of nooks and crannies. We saw Lion's Mane Jellies, a few tautog, etc. Both of these provide useful landmarks underwater if you've never been to the site before.
I've only been to this site in April and May. Marine life was rather limited, but may be different in mid-summer.
Hope this helps.