Include the header with #include at the top of your file. Then declare with types: map<int, string> m; creates an empty map where keys are integers and values are strings. You can initialize with values immediately: map<string, int> ages = {{"Alice", 25}, {"Bob", 30}}; sets two entries at declaration time.
The curly braces nest to define key-value pairs. The first type in the template is always the key, the second is the value. Keys must support the < operator for comparison, which all built-in types do automatically.