The information alread given by Vidaloco is very good. White vinegar will work too. It's the acid that does it. But apple vinegar taste better (in case you're looking to eat the horse's frog
I wish I could give you a good picture of thrush, but it can build up in different ways/areas. The informatin already given provides a good discription (dark, gooey and foul smell). If it's not possible to cut it away and leave it exposed to the air (e.g. It's in a deep crevice) then you can pack it with cotton or gauze soaked with tea tree oil. Change out the soaked packing every 4 days. Changing it that soon might not be neede and one good soaking left for a week or 10 days might work, but I'm a bit anal about thrush and tend to do overkill.
To often my new horses have come with it.