private void button1_Click(object sender, EventArgs e)
        {
            
            bw = new BackgroundWorker();
            bw.DoWork += (obj, ea) => TasksAsync(1);
            bw.RunWorkerAsync();
            //здесь подождать пока не выполнится поток
/////продолжить выполнение кода, ниже код
        }

private Task MyAsync()
{
	return Task.Run(() =>
		{
			// код в потоке
			...
		}
		);
}

ButtonsClick()
{
	await MyAsync();
}

 private void button1_Click(object sender, EventArgs e)
        {
            MyAsync();
            await MyAsync();
        }

       private ASYNC void button1_Click(object sender, EventArgs e)
        {
            progressBar1.Style = ProgressBarStyle.Marquee;
            progressBar1.MarqueeAnimationSpeed = 30;
            MyAsync();
            await MyAsync();
            progressBar1.Style = ProgressBarStyle.Continuous;
            progressBar1.MarqueeAnimationSpeed = 0;
        }
    }
}

namespace WindowsFormsApplication12
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
            progress();
        }

        private void progress()
        {
            progressBar1.Style = ProgressBarStyle.Continuous;
            progressBar1.MarqueeAnimationSpeed = 0;
        }
   private Task MyAsync()
{
	return Task.Run(() =>
		{
			  ProcessStartInfo psi;
                psi = new ProcessStartInfo("cmd", @"/c echo hello word" + "&" + "pause");
                Process.Start(psi).WaitForExit();
		});
		
}
               
        private async void button1_Click(object sender, EventArgs e)
        {
            progressBar1.Style = ProgressBarStyle.Marquee;
            progressBar1.MarqueeAnimationSpeed = 30;
          await MyAsync();
            progressBar1.Style = ProgressBarStyle.Continuous;
            progressBar1.MarqueeAnimationSpeed = 0;
        }
    }
}