> The trackball command in tasker has only this selections:
> up, down, left, right, press

Yes, it's not a trackball, it's more a cursor pad with a select button
in the centre.

> So how do I have to use this?

The dpad changes the current focused UI element, which is illuminated
orange if there is one.

> on the screen. I tested in doing some trackball up commands and then
> one trackball press. I'd expect to see the system pull  down menu from
> android but nothing happened.

You need Input / Button (Menu) to call up the menu.

Then put in a Task / Wait action to give the menu time to show. Then
use Dpad down
to select a menu item then Dpad centre to select.

Pent