// create map
let map = new Map<string, number>();

// set entities
map.set("Ann", 25);
map.set("Seth", 32);
map.set("Kate", 27);

// get entities
let value1 = map.get("Ann");
console.log("Ann age: " + value1); // Ann age: 25

let value2 = map.get("Seth");
console.log("Seth age: " + value2); // Seth age: 32

let value3 = map.get("Kate");
console.log("Kate age: " + value3); // Kate age: 27

// siz of map
let size = map.size;
console.log("map size: " + size); // map size: 3

Output:

Ann age: 25
Seth age: 32
Kate age: 27
map size: 3

Run this example online:

codepen

3. Most important methods of Map:

map.set() - add key-value pair to Map
map.get() - retrieve value by key from Map
map.delete() - delete key-value pair by given key from Map
map.has() - check if there is a value for given key - return true / false
map.size() - size of the map, number of key-value pairs in Map

Note about map.set() method.
In other languages or self implemented data structures to add key-value pair to Map the method is named: put, add or set.

Reference:

Mozilla docs - Map