Use activities to represent your actual interactions with your customers such as phone calls, meetings, presentations, etc. The built-in activity reports in Nutshell make it easy to track the times you interact with customers. Use an activity if you need to report on your contact with customers and leads.

Tasks are built for things that you need to do in the future but are not actual events with your customers. Think of tasks like post-it notes that you'd throw away after you take care of it. Use a task for things you need to do but don't need to track or report on later.