1) The document introduces equations and equality through a series of activities exploring the meaning of the equal sign and how to balance equations.
2) Key concepts covered include understanding that both sides of an equation must be equal, using inverse operations to find unknown values, and representing equations using virtual balances.
3) The activities scaffold students' understanding by having them first explore equality in different contexts, then apply operations to balances both virtually and with physical manipulatives, before solving for unknown values in equations.