How to show progress dialog in Android?

ProgressDialog pd = new ProgressDialog(yourActivity.this);
pd.setMessage("loading");
pd.show();

And that's all you need.

You better try with AsyncTask

Sample code -

private class YourAsyncTask extends AsyncTask<Void, Void, Void> {
    private ProgressDialog dialog;

    public YourAsyncTask(MyMainActivity activity) {
        dialog = new ProgressDialog(activity);
    }

    @Override
    protected void onPreExecute() {
        dialog.setMessage("Doing something, please wait.");
        dialog.show();
    }
    @Override
    protected Void doInBackground(Void... args) {
        // do background work here
        return null;
    }
    @Override
    protected void onPostExecute(Void result) {
         // do UI work here
        if (dialog.isShowing()) {
            dialog.dismiss();
        }
    }
}

Use the above code in your Login Button Activity. And, do the stuff in doInBackground and onPostExecute

Update:

ProgressDialog is integrated with AsyncTask as you said your task takes time for processing.

Update:

ProgressDialog class was deprecated as of API 26

To use ProgressDialog use the below code

ProgressDialog progressdialog = new ProgressDialog(getApplicationContext());
progressdialog.setMessage("Please Wait....");

To start the ProgressDialog use

progressdialog.show();

progressdialog.setCancelable(false); is used so that ProgressDialog cannot be cancelled until the work is done.

To stop the ProgressDialog use this code (when your work is finished):

progressdialog.dismiss();`