How to display a one time welcome screen?

Here’s some code from my application which does just that.

In your activity:

SharedPreferences mPrefs;
final String welcomeScreenShownPref = "welcomeScreenShown";

/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.main);

    mPrefs = PreferenceManager.getDefaultSharedPreferences(this);

    // second argument is the default to use if the preference can't be found
    Boolean welcomeScreenShown = mPrefs.getBoolean(welcomeScreenShownPref, false);

    if (!welcomeScreenShown) {
        // here you can launch another activity if you like
        // the code below will display a popup

        String whatsNewTitle = getResources().getString(R.string.whatsNewTitle);
        String whatsNewText = getResources().getString(R.string.whatsNewText);
        new AlertDialog.Builder(this).setIcon(android.R.drawable.ic_dialog_alert).setTitle(whatsNewTitle).setMessage(whatsNewText).setPositiveButton(
                R.string.ok, new DialogInterface.OnClickListener() {
                    public void onClick(DialogInterface dialog, int which) {
                        dialog.dismiss();
                    }
                }).show();
        SharedPreferences.Editor editor = mPrefs.edit();
        editor.putBoolean(welcomeScreenShownPref, true);
        editor.commit(); // Very important to save the preference
    }

}