1. Language varies based on factors like context, audience, purpose, and social situation. It varies between spoken and written forms as well as between everyday and specialized contexts. 2. Varieties include differences between local dialects, globalized forms of the language, and languages that develop between distinct language groups like pidgins and creoles. 3. Registers refer to the adjustments speakers make in their vocabulary, grammar, and style depending on circumstances. Both variety and register help account for the multiple ways language is used.