For instance, if you're posting about an Open House or Garage Sale, this would be best to add to the Classifieds. If you're posting an organized event, (fundraiser, etc.) then the Calendar would be better. Where appropriate, feel free to add to both the Calendar and the Classifeds to reach people in different ways.
When you post an event, there may be upcoming events before yours. The daily newsletter only displays a few events at a time, so the event will be shown as the date approaches. If you would like to bring awareness to your event weeks before, consider making a post on the Classifieds. This will allow you to raise awareness before the week of the event.