If you look at tree stumps, logs and fallen branches of deciduous trees (as I like to do) you will often find bracket fungi growing on them. In some cases the fungus will have got in to the tree whilst still alive and killed it, in others the fungus colonises the dead wood and has started the rotting process which will eventually see it return to just plain earth. The hairy curtain crust (Stereum hirsutum) is one of the latter.
This is a very common species, indeed one of the most common fungi you will find. Along with many-zoned polypore it accounts for something like two-thirds of all bracket fungi specimens you will encounter. It can be told from many-zoned polypore, however, by the dustincly yellowish appearance when the bracket is first emerging as a fruiting body. It is a bit harder to tell them appart when they have done their job of releasing spores and have dried up. I have no idea why it is called 'hairy', the book I have does not describe any obvious 'hairy' features but then, that is common names for you!
Found all year round, do not bother to try eating it, it is as tough as old boots and best left alone!