this is a skill you need if you are a man or know one. it is immensely helpful. i do not possess this skill. my husband, thankfully, can tie like a million different kinds of knots (he worked in the macy's men's department for a little while when we were in college, and also has a semi-foreign family that places importance on this kind of thing). my father had a dinner dance to go to for my mother's work agency on sunday night, and when we were over during the day, he realized that he had a new tie to wear for the occasion but it was (obviously) not tied! since my father works in a very blue-collar field, he never has to wear ties and his dress-up gear usually involves a sweater and a semi-clean pair of pants, excepting Sons of the American Legion functions for which he has to wear a tie with his dress colors (but it's already pre-tied). thankfully my husband knew how to tie his tie with the right knot for the occasion, and at the right length for my father, who is a good deal shorter than him. but my mom confessed that she didn't know how to tie a necktie either; if we hadn't been over, she would have gone on the internet to find out how to do it. so really, this is for mom. and for me. i may need this skill someday, and hubs isn't always going to be around to help my very sorry self.
Tie-a-tie.net has very good, easy-to follow instructions and seems to be updated at least semi-regularly (but really, how often does tie tying change?). there is also other useful men's dress-up information here, like how to properly fold a pocket square. there's even a tie blog. yeah. really.
this nifty little page is from a former MIT student, but has a handy, printable cheat sheet that includes the ever-classy bow tie. i love bow ties and find them to be a terribly underutilized accessory. whenever i watch the twilight zone (or mad men, obvs) i always long for their stylish menswear.
anyway, hope this helped!