On Lycanthropy
The Strains
There are two main kinds of lycanthropy: infectious and hereditary. They closely resemble each other, and mainly differ in terms of transmission.
Infectious Lycanthropy (IL) can be passed on by the bite of a transformed werewolf with IL, or via the bodily fluids of a werewolf or carrier near the full moon.
If an infected person does not become a werewolf, they either become a carrier or are killed by the infection. The infection can be eradicated by a carrier's body over time.
Hereditary Lycanthropy (HL) is, well, hereditary. Passed from parent to child, but not sex-linked. It can become active at any age, or stay dormant a person's entire life.
On Both
Because of slight mutations between individual strains, what is a weakness to one werewolf may have no effect on another.
It can be difficult to determine which kind of lycanthropy a werewolf has. In the absence of a specific diagnosis, all lycanthropes are assumed to be IL.
The Change
It almost always compulsory to change on a full moon. Aside from the full moon, change is usually voluntary, although other stimuli can trigger the urge.
Changing is quick and painless when done right, but rough on the body.
Changing too much can cause a host of problems.
One of the worst things that can happen is being caught halfway. It is extremely dangerous, since a werewolf could die from horrific malformations (e.g. mix-and-match organs), although a werewolf can get by with benign if embarrassing changes (e.g. human body but wolf ears) if they're lucky.
Werewolves are usually in control of themselves when changed, albeit altered. However, any werewolf has the chance of going "wild" -- which can range from acting like an animal, to rampaging and attacking indiscriminately.
The actual form of a transformed werewolf can be inconsistent, ranging from a monster-sized wolf to an almost-bipedal wolf-monster. The same werewolf can take more than one form, and ultimately can't choose what form they'll take. Many werewolves only occupy a limited part of the possible range of changes.
Werewolves have accelerated (but not death-defying) healing, increased resistance to disease, and big appetites. This is significantly greater in wolf form than in human form, although notable in either form compared to a normal human. (The appetite still has nothing on the appetite of someone with parasitic Innocence in canon.)