Muggles' Guide to Harry Potter/Magic/Serpensortia

Overview
Serpensortia makes a snake appear from the end of the caster's wand. Malfoy uses this spell against Harry during a duel in Harry Potter and the Chamber of Secrets.

Extended Description
This is a major plot point, as it is the first time that Harry has had to use Parseltongue in front of wizards, and while we have seen it before, neither he nor we understand its significance.