In Configuration->Queue process you need to enable the cron. Click on the button create/edit cron task and in the next screen you can enable it.
You can check if the cropn works by pasting your cron url in your browser addres bar. You should see a messgae that Acymailing was triggered. If you see this it means your cron is functioning.
In Configuration->Queue process you can always see when Acymailing was trigered for the last time. It's at tyhe bottom of the screen.