You have already gotten some useful answers, but others I disagree with. You can kill insects several different ways, depending on species, size, and other considerations. Butterflies, especially larger ones, can be pinched on the thorax between thumbnail and forefinger. Smaller butts and moths should be dispached in a killing jar. Some insects can be frozen, but you may need to keep them in the freezer for a day or more. They will thaw quite quickly at room temperature, and will gradually become active if you didn't keep them in long enough. You can make a killing jar by pouring plaster of Paris into a jar and letting it dry. Then use ethyl acetate to saturate the material just before use. >>Stay away from cyanide.<< Spreading butterflies requires a pinning board made of soft material (to accept pins), with a groove in the middle to accomodate the insect body. Push a suitable-sized pin (frequently #2) centered and straight through the thorax; center the insect in the groove and push down until the spread wings contact the board. Use the smallest pins possible to gently manipulate the wings so that the forewings' hind edge is perpendicular to the body. Then bring the hind wings into position so that they are spread, but not hidden by the forewings. Push a pin through the point where the two wings overlap at the base to hold them. You can place microscope slides on the wings to hold them flat until they dry. Especially larger butterflies must dry for at least a day, maybe two or more, depending on humidity. This whole process takes a bit of practice and is better attempted on larger specimens at first. Try to include members of as many different families of insects as possible. The **most important part** of your collection is an accurate and detailed label for each specimen. The label must indicate the location, date, and collector. Here's an example of a four-line label: / USA, AZ, Pima Co. / Mt. Lemmon / 23 Aug 2009 / Coll. John Doe /. NOTE: A specimen without a label is virtually worthless! You can find supplies and information on the internet, or perhaps from a university entomology department or museum, or perhaps from a local entomologist. Good luck!