This trailhead is accessible only by water; the usual method is to hire a water taxi from Homer. The taxis do not run in loops like a bus or mass-transit ferry, so you do need to arrange (and pay for) transport in advance.
Although you can reach several trails from here, the most popular by far is the hike to the shore of Grewingk Lake, with Grewingk Glacier on the other side. If you plan to do that hike, make sure your pick-up plans with the water taxi company are very explicit. Most hikers will ask to be dropped off at this trailhead (Glacier Spit) but picked up at another trailhead (Saddle Trail), as you can link the two trails together into a short, but beautiful, thru-hike.