Regarding the usage of SemaphoreSlim with Async/Await

i am not advance developer. just trying to have hold on task library just googling.i never use this class SemaphoreSlim so i like to know what it does. here i go through a code where SemaphoreSlim is used with Async & Await but do not understand because i am not very advance developer. so here i am pasting the code. if possible please some one help me to understand the below code.
1st set of code

await WorkerMainAsync();

async Task WorkerMainAsync()
{
  SemaphoreSlim ss = new SemaphoreSlim(10);
  while (true)
  {
    await ss.WaitAsync();
    // you should probably store this task somewhere and then await it
    var task = DoPollingThenWorkAsync();
  }
}

async Task DoPollingThenWorkAsync(SemaphoreSlim semaphore)
{
  var msg = Poll();
  if (msg != null)
  {
    await Task.Delay(3000); // process the I/O-bound job
  }

  // this assumes you don't have to worry about exceptions
  // otherwise consider try-finally
  semaphore.Release();
}

first WorkerMainAsync will be called and there SemaphoreSlim is used. why 10 is passing to SemaphoreSlim constructor.

again when control goes out from while loop.

what ss.WaitAsync(); does ?

`DoPollingThenWorkAsync()` function expecting `SemaphoreSlim` but not passing anything when it is called.......is it typo ?

why they use await Task.Delay(3000);

they can use simply Task.Delay(3000) but why they use await here.
2nd set of code for same purpose

async Task WorkerMainAsync()
{
  SemaphoreSlim ss = new SemaphoreSlim(10);
  List<Task> trackedTasks = new List<Task>();
  while (DoMore())
  {
    await ss.WaitAsync();
    trackedTasks.Add(Task.Run(() =>
              {
                DoPollingThenWorkAsync();
                ss.Release();
              }));
  }
  await Task.WhenAll(trackedTasks);
}

void DoPollingThenWorkAsync()
{
  var msg = Poll();
  if (msg != null)
  {
    Thread.Sleep(2000); // process the long running CPU-bound job
  }
}

here task & ss.release is added to list....just really do not understand after adding task to list how they can run?

trackedTasks.Add(Task.Run(async () =>
              {
                await DoPollingThenWorkAsync();
                ss.Release();
              }));

looking for good explanation & help to understand two set of code.thanks