You learned to declare variables with let (changeable) and const (fixed). You explored primitive types: string, number, boolean, null, undefined, symbol, and bigint.
You discovered truthy/falsy values and why === is safer than ==. You practiced type coercion and learned to check types with typeof.
Key rule: use const by default, === for comparisons, and Number.isNaN() for NaN checks. These habits prevent common JavaScript bugs.