what is a good site to learn magic tricks such as coin and card tricks for free?

The best site for getting guides and learning for free is the public library. 793.8 is the Dewey Decimal listing for books on how to do magic.

Among the books I’d recommend to a beginner are:

any of the self-working books by Karl Fulves
any of the Tarbell Course in Magic by Harlan Tarbell
Complete Course in Magic by Mark Wilson
Now You See It by Bill Tarr
Card College (or Card College Light, Card College Lighter, Card College Lightest) by Roberto Giobbi

If you’re able to afford instructional DVDs, start with those by Michael Ammar. He’s the best teacher on video. His style isn’t flashy, but you’ll come away with solid skills. Stay away from youtube until you have a bit more background. There is some great material there, but you have to wade through a lot of garbage. Bad instruction is worse than no instruction.

Ellusionist and Penguin magic are on-line sites that do offer a few free video lessons which can help get you started. Don’t stop with them, and recognize that they are using the freebies as a way to get you inside to buy.

If you really get into doing magic, check out the websites for the Society of American Magicians, or the International Brotherhood of Magicians. They have lots of local chapters. Perhaps you can find one near you to attend. Learning from other magicians is a great way to improve your skills.