aas - anabolic (tissue growth) and androgenic (male characteristic) steroids
frankly its what aas do. some aas give rise to other aas when in the body, which you alluded to when you mentioned finasteride, (finasteride will stop testosterone being changed into dihydrotestosterone, a very anabolic but also very androgenic hormone) which then trip off various receptors in various tissues - in this case on the hair follicle, or in certain skin cells, giving rise to a new hair follicle, or however it actually happens) and you get your effect.
thats it
cheers