/// <summary>
/// Registers a background task in the system waiting to trigger
/// </summary>
/// <param name="taskName">Name of the task. Has to be unique</param>
/// <param name="taskEntryPoint">Entry point (Namespace) of the class (has to implement IBackgroundTask and has to be in a Windows Runtime Component) to start</param>
/// <param name="trigger">What has to be triggered to start the task</param>
/// <param name="condition">Optional condition. Can be null</param>
/// <param name="recreateIfExists">Should the Task be recreated if it already exists?</param>
/// <returns></returns>
public BackgroundTaskRegistration RegisterTask(string taskName, string taskEntryPoint, IBackgroundTrigger trigger, IBackgroundCondition condition = null) {
    Debug.WriteLine("Try registering task: " + taskName);

    var builder = new BackgroundTaskBuilder {
        Name = taskName,
        TaskEntryPoint = taskEntryPoint
    };

    builder.SetTrigger(trigger);

    if (condition != null) {
        builder.AddCondition(condition);
    }

    try {
        var task = builder.Register();
        Debug.WriteLine("Task successfully registered");
        return task;
    } catch (Exception exception) {
        Debug.WriteLine("Error creating Task: " + exception);
        return null;
    }
}

/// <summary>
/// Gets a BackgroundTask by its name
/// </summary>
/// <param name="taskName">Name of the task to find</param>
/// <returns>The found Task or null if none found</returns>
public BackgroundTaskRegistration TaskByName(string taskName) =>
       BackgroundTaskRegistration.AllTasks.FirstOrDefault(x => x.Value.Name.Equals(taskName)).Value as BackgroundTaskRegistration;

public sealed class BackgroundTask : IBackgroundTask {

    private BackgroundTaskDeferral _deferral;

    /// <summary>
    /// Registers the listener to check if the button is pressed
    /// </summary>
    /// <param name="taskInstance">An interface to an instance of the background task. The system creates this instance when the task has been triggered to run.</param>
    public async void Run(IBackgroundTaskInstance taskInstance) {
        _deferral = taskInstance.GetDeferral();

        //Do async operations here

        _deferral.Complete();
    }
}

private bool IsTaskRegistered(string taskName) =>
        BackgroundTaskRegistration.AllTasks.Any(x => x.Value.Name.Equals(taskName));

var trigger = new ApplicationTrigger();
TaskHandlerMentionedInThisTutorial.RegisterTask(TaskName, entryPoint, trigger, null, true);    
await trigger.RequestAsync();

/// <summary>
/// Unregister a single background task with given name
/// </summary>
/// <param name="taskName">task name</param>
/// <param name="cancelTask">true if task should be cancelled, false if allowed to finish</param>
public void UnregisterTask(string taskName, bool cancelTask) =>
    BackgroundTaskRegistration.AllTasks.First(x => x.Value.Name.Equals(taskName)).Value?.Unregister(cancelTask);

/// <summary>
/// Unregister an active group of background tasks, which name contains given string
/// </summary>
/// <param name="taskNamePart">part of the task name</param>
/// <param name="cancelTask">true if tasks should be cancelled, false if allowed to finish</param>
public void UnregisterTasks(string taskNamePart, bool cancelTask)
{
    foreach (var task in BackgroundTaskRegistration.AllTasks.Where(x => x.Value.Name.Contains(taskNamePart)))
        task.Value.Unregister(cancelTask);
}

The background task are a great way to perform some work while your application is not running. Before being able to use then , you will have to register them.

Here is a sample of a background task class including the registration with a trigger and a condition and the Run implementation

public sealed class Agent : IBackgroundTask
{    
    public void Run(IBackgroundTaskInstance taskInstance)
    {
        // run the background task code
    }
    
    // call it when your application will start.
    // it will register the task if not already done
    private static IBackgroundTaskRegistration Register()
    {
        // get the entry point of the task. I'm reusing this as the task name in order to get an unique name
        var taskEntryPoint   = typeof(Agent).FullName;
        var taskName         = taskEntryPoint;
        
        // if the task is already registered, there is no need to register it again
        var registration            = BackgroundTaskRegistration.AllTasks.Select(x => x.Value).FirstOrDefault(x => x.Name == taskName);
        if(registration != null) return registration;
                        
        // register the task to run every 30 minutes if an internet connection is available
        var taskBuilder             = new BackgroundTaskBuilder();
        taskBuilder.Name            = taskName;
        taskBuilder.TaskEntryPoint  = taskEntryPoint;
        taskBuilder.SetTrigger(new TimeTrigger(30, false));
        taskBuilder.AddCondition(new SystemCondition(SystemConditionType.InternetAvailable));
        
        return taskBuilder.Register();
    }
}