A field type establishes what a value means and what the platform can validate or calculate. Number and currency fields support arithmetic; percent fields express a percentage. A checkbox has a true or false value, while an empty optional number is different from zero. Dates have no time of day; date/time values need time-zone interpretation.
Use contact types for email, phone, and web addresses instead of treating every value as unrestricted text. A long text area fits a narrative, but a bounded text field fits an external reference. Auto-number provides a generated sequence rather than a quantity. Choose the type from the required behavior, then set precision, length, defaults, and requiredness deliberately. The exercises cover both individual fields and a small typed record schema.