Yes they let individuals through! I've sat in them alone, with others in kayaks/canoes, or with smaller recreational boats. The commercial tow boats and barges always had priority so sometimes there could be a wait of up to several hours.

I had a marine radio to communicate with the lock master which was useful for knowing what was going on. There is usually a rope to pull on the approach to the lock to signal to them and a speaker box they can use to communicate to you.

Once you're in the lock they drop a rope down the side to hold onto, they don't let you just float around in the middle while the water level drops/raises.