In the old European folklore there were many different characteristics that were thought to be able to distinguish a werewolf to normal human being. These included both eyebrows meeting in the middle, curved nails, low set ears and a swinging stride. However in wolf form there were very few differences from a normal wolf. One main one though is the fact that a werewolf will have no tail. This is thought to link to witches for when they are in their own animal form.
There are thought to be a few different ways on how a werewolf turns. The most common is one is on a full moon. This came about from French and German folklore, it was thought that if a man or woman was to sleep outside on certain Wednesdays and Fridays on a summer night with the full moon shining on their face that they would be able to turn. One of the more simpler way was to strip of clothing and wear a wolfskin belt. Another was to drink rain water from the footprint of that animal was said work. Remedies to help get rid of a werewolf include the medicinal use of wolfsbane, exorcisim or some slightly more painful methods.
Since the 1900's Werewolves have become more popular in modern fiction writing. It was actually in 1935 that it was thought that silver would be able to harm a werewolf. It is also said in Bram Stoker's 'Dracula' that a werewolf can only be harmed a 'sacred bullet' and they can only change forms during the night and not day. Also thanks to modern fiction it is thought that werewolves have heightened senses such as speed and strength. Each film or book depicts werewolves to look slightly different. For instance in 'Werewolf in London' the main character is said to keep most of his main features, while in Stephanie Myers 'Twilight' Jacob Black turns into a slightly larger version of a normal wolf. Another version is in J.K.Rowling's 'Harry Potter' series, Professor Lupin turns into a wolf form but walks on his two hind legs but has none of his normal features.
There is a medical condition called Clinical Lycanthropy. This is a rare psychiatric condition where the person thinks they can transform/ have transformed into an animal.