how to tie a string on a classical guitar?

Answer 1

I always had my strings tied around the bridge,
like this site:
http://www.smshobby.com/Tools/how_to.html
To do that you feed the string through the hole, bring the short end round the string and wrap it round itself. The Nylon only strings need about 5 twists, the metal and nylon strings can do with just 2.
Different picture:
http://thurmanator.hypermart.net/instruments/classic/lopez/lopbridge.jpg
(All strings did get the same amount of twists.)
http://thurmanator.hypermart.net/instruments/classic/Montflam/montflambridge.jpg (More like what I was taught.)

This site has a knot on the one side of the bridge:
http://emedia.leeward.hawaii.edu/Frary/buying_a_classic_gtr.htm

If you have a guitar with pegs in the bridge or if you want to use the knot on one side of the bridge method, make a double overhand or thumb knot, ( or triple with one more tuck):
http://www.animatedknots.com/stopper/index.php?LogoImage=LogoGrog.jpg&Website=www.animatedknots.com
Pull your knot real tight and keep an eye on it till the string is tightened, string will not keep this knot well.
With pegs you should use the special strings with the little rings at the end.

Answer 2

Check out YouTube. Type in what you asked here...the search will give you plenty. Good luck.