Task.Run() / Task.Delay()

using System.Threading.Tasks;

// Runs a delegate on a background thread.
Task task = Task.Run(() => process);
Task<T> task = Task.Run(() => processWithReturnValue);

// Waits asynchronously for the specified number of milliseconds.
await Task.Delay(milliseconds);

// Waits until all tasks have completed.
await Task.WhenAll(task1, task2, task3);

// Waits until the first task completes.
Task first = await Task.WhenAny(task1, task2, task3);

using System;
using System.Collections.Generic;
using System.Threading.Tasks;

// Run a background task with Task.Run.
Task<int> bgTask = Task.Run(() =>
{
    int sum = 0;
    for (int i = 1; i <= 100; i++) sum += i;
    return sum;
});
Console.WriteLine(await bgTask); // 5050

// Use Task.Delay to sleep asynchronously (alternative to Thread.Sleep).
Console.WriteLine("Start");
await Task.Delay(1000); // Wait 1 second
Console.WriteLine("1 second later");

// WhenAll: run multiple tasks in parallel and wait for all to complete.
Task<string> t1 = Task.Run(async () => { await Task.Delay(100); return "Task 1"; });
Task<string> t2 = Task.Run(async () => { await Task.Delay(200); return "Task 2"; });
Task<string> t3 = Task.Run(async () => { await Task.Delay(50);  return "Task 3"; });

string[] results = await Task.WhenAll(t1, t2, t3);
Console.WriteLine(string.Join(", ", results)); // Task 1, Task 2, Task 3

// WhenAny: get the first task to complete (timeout example).
Task<int> longTask = Task.Run(async () => { await Task.Delay(5000); return 42; });
Task timeoutTask = Task.Delay(1000);

Task finished = await Task.WhenAny(longTask, timeoutTask);
if (finished == timeoutTask)
    Console.WriteLine("Timed out");
else
    Console.WriteLine($"Done: {longTask.Result}");

Task.WhenAll() runs multiple asynchronous operations in parallel and waits for all of them to finish. This reduces total wait time compared to awaiting each task sequentially.

Using task.Result or task.Wait() inside an async method can cause a deadlock. Always use await inside asynchronous code. If you need to retrieve a result synchronously, consider using Task.FromResult().

For the basic async syntax, see async / await. For cancellation in async operations, see CancellationToken.