The goal of this guide is to address a major environmental dilemma: worldwide habitat destruction and the disappearance of species. This guide is one of six that are included in the Habitat Ecology Learning Program (HELP), a holistic life science curriculum that involves students in an in-depth study of ecology. HELP includes six teaching guides and focuses on five habitats: rain forests, temperate forests, deserts, grasslands, and wetlands. "How Nature Works" provides an overview of key ecological concepts that enable students to understand the subsequent habitat modules. The teaching guide contains informative essays on relevant issues, specific background information on plants and animals, detailed lesson plans, a scope and sequence chart for the lessons, and answers to student questions. Student handouts that may be copied are included. The units of study included in this guide are: (1) What is Ecology; (2) Climate, Seasons, and Habitat; (3) The Taxonomic Shuffle; (4) Adept Adaptations; (5) The Food Web Connection; (6) Energy by the Numbers; and (7) The Big Squeeze. (DDR)