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Maps work the same way — read-only Map<K, V> and mutable MutableMap<K, V>:

val ages = mapOf(
    "Alice" to 30,
    "Bob" to 25,
)

println(ages["Alice"])              // 30
println(ages.containsKey("Carol")) // false

val mutable = mutableMapOf<String, Int>()
mutable["Carol"] = 40
mutable.remove("Carol")

The to operator creates a Pair<K, V>. The mapOf function takes any number of pairs.

map[key] returns V? — null if missing. The getOrDefault(key, default) form is convenient for counters:

val counts = mutableMapOf<String, Int>()
for (w in words) {
    counts[w] = counts.getOrDefault(w, 0) + 1
}