What Happens If A Garden Snake Bites You?

Since there's no such thing as a "garden snake", there's no way to answer that question.
There IS a GARTER Snake, which is harmless to humans.  They DO have mild venom, and enlarged teeth at the back of their mouths, but the venom is generally too weak to produce results in humans unless you are allergic to some of the proteins in it.  For the most part, you'd have some small punctures or scratches, like a small briar scratch, that might bleed or sting a bit.  If you were allergic this would begin to swell and itch, and you'd probably break out in hives or have trouble breathing, just as you would with any other allergic reaction, but such allergies are rare.