A map stores pairs of keys and values. You give it a key, it returns the associated value. Think of a dictionary: you look up a word (key) to find its definition (value). In C++, you write Maps keep keys sorted automatically.
Looking up a key takes time. You'll use maps whenever you need fast lookups by a custom key. Understanding this concept deeply will help you write better code. Practice with examples until the pattern becomes automatic.
Review earlier sections if anything is unclear. Building on solid foundations makes advanced topics easier.