Heather -- There are many silver coins with the Indian and Buffalo pattern. They are all marked with the amount of silver they contain. Yours has 1 troy ounce of pure (0.999) silver. For a similar coin, but with 2 troy ounces of silver, see this page:
Your 'coin' is not really a coin, since it cannot be used in commerce. Officially, it is a 'medal,' but it is still worth something. It is worth its weight in silver. If you look on the internet, you will find silver is selling today for about $18 US dollars per troy ounce. So that's what your medal is worth, $18. If you sold it to a collector, he or she would pay about $18, maybe a little more, maybe a little less.
BTW, when dealing with precious metals, like silver and gold, one troy ounce is the same as one ounce, the 'troy' is understood.