Tarragon is a fairly pungent herb that is most commonly found in French cooking. It has an aniseed taste like liquorice and if you've not cooked with it before you might want to go light with the amount you use as it's fairly pungent.
When using fresh tarragon you need to pull the leaves from the stems and wash well. You can then finely chop the leaves and add to your dish or use as a garnish.
Dried tarragon can also be used. As dried herbs are stronger than fresh, reduce the amount by half. You will also need to add it earlier on in the cooking process. Sprinkle it into the pan when you add the stock to allow the flavour more time to release its unique taste.