On the Information tab you set your trigger. Let's assume you trigger the Automation once a day at a given time.
On the Conditions tab you can set rules that will determine when the Atomation is triggered it should only be executed when certain conditions are met. See it as an extra parameter to the trigger.
On the Actions tab you specify what you want to do with the contacts you are about to import. For example, you can subscribe them to a list.
Here comes the fun part. Go to the Action targets tab and select "Import from database" (for this the Universal Filter add-on must be installed and enabled)
Select the table #_contact_details and use the WHERE to exclude contacts that have no mail address.
Match the mail and name fields between the contact table and Acymailing and you're good to go.