Spiders are arachnids, not insects. Other members of the arachnid family include scorpions, mites, ticks, and harvestmen. Spiders have 8 legs while insects have 6.
Spiders don't have antennae while insects do. Spiders are found on every continent of the world except Antarctica. There are around 40000 different species of spiders. Most spiders make silk which they use to create spider webs and capture prey. Abandoned spider webs are called cobwebs.
Most spiders are harmless to humans but a few spider species, such as the black widow, can bite humans and inject venom. Deaths from spider bites are rare, however.