Take a bacteria sample from a desired location. Many classroom experiments involve collecting samples from doorknobs or people's hands. Otherwise, buy a specific type of bacteria from a supplier.
Mix all the NaCl, tryptone, yeast extract, agar and water in a beaker. This combination serves as the culturing medium for the bacteria.
Autoclave the mixture for 30 minutes at 121 degrees Celsius. Let it cool off some.
While the mixture is still somewhat warm, distribute it evenly it into the media plates and let it set at room temperature overnight.
Sterilize the end of a wire loop by holding it over a Bunsen burner until it glows red.
Prevent the end from touching anything as the loop cools off again. This will take a few seconds.
Scoop a sample of bacteria onto a media plate with the sterilized wire loop.
Gently spread the bacteria onto the media plate in a broad zig-zag pattern, taking care not to completely penetrate the culture medium with the wire loop.
Incubate the plates for a day or two at 37 degrees Celsius, away from sunlight and direct heat. (The top of a refrigerator can work well.)
Observe the culture with a microscope and conduct any tests or experiments as needed.
Clean the plates with bleach to kill the bacteria when you've finished observing the bacteria.