Lava and You was a training film shown in "Volcano" encouraging you to "duck and cover" to protect yourself from lava. Chef points out that this is complete rubbish and those who do "duck and cover" are killed. This is a parody of the types of films used during the 1950s for educational training films usually depicting hygiene, social etiquette, survival safety and moral lessons.
The film was based on a real government initiative which encouraged people to duck and cover in order to protect themselves in the event of a nuclear detonation. The clip can be found on South Park Studios here.