Rust: How do you implement async functions?

1async fn fetch_data() -> String {
2    // Async operation
3    tokio::time::sleep(std::time::Duration::from_secs(1)).await;
4    String::from("data")
5}
6
7#[tokio::main]
8async fn main() {
9    let data = fetch_data().await;
10    println!("{}", data);
11}

1let future = async {
2    42
3};
4
5let result = future.await;

1let (a, b) = tokio::join!(fetch_a(), fetch_b());