The snakes you are most likely to see moving around in daytime are the Garter Snake and the Green Snake.Most Garter Snakes will try to bite when first picked up. The strike is pretty quick - you won't likely get any warning. The bite is more a surprise than anything else. The little teeth can make needle-like punctures in the skin, and the snake may work its jaws back and forth to get a better grip. If you still don't let go, they usually release (from the vent) a really smelly fluid. Imagine yourself as a Great Blue Heron with a mouthful of snake - the fluid is supposed to make you let go in disgust. You can pick up a snake and avoid a bite by holding it with your thumb and forefinger, behind the neck. Support the heavy body and tail with your other hand.
Green Snakes are very wiggly when warm. Often they only quiet down when they can wrap tightly around your fingers.
Ringnecks and Redbellies hide during the day. You'll likely only come across them if you lift rocks, boards or other sheltering things.
Do not try to keep anything but the Garter Snake for more than a day. Green Snakes rarely eat well in captivity. Ringnecks and Redbellies may, IF you go to the trouble of getting live Red-backed Salamanders and slugs for them.
Keep Garter Snakes in a dry environment, with a jar of water big enough for them to go in if they want to. A good depth of pine needles makes an interesting habitat - you'll see the snake heads popping up out of the needles. A light source for sunning is good, too. Feed them live earthworms, and let them go as soon as they stop feeding well, stop being active in daytime, or at least by September so they have plenty of time to find a hibernation site.
While you have the snake, look for the nostrils, ear holes, eyelids (trick question). Watch the snake's body as its single long lung expands and contracts. Feed it and watch the jaws work to hold the prey and slide it down into the stomach. Let the tongue tickle your cheek. Turn it over and see how the belly scales overlap from front to back, like roof shingles, to help with movement. You can put a Garter Snake in water and watch it swim across the surface, just make sure it has a place to dry afterwards.
If the eyes get opaque and bluish, the snake is preparing to shed its skin. Be sure there is something rough available, like twigs, for it to rub against to get started. The shed skin will dry out and can be kept forever. If you're lucky, the head scales will come off intact and you can see the form of the eyes, and every individual scale.
If you need advice, try the Museum or the Herpetoculture Society.