In it's simplest terms, Activities are any type of form used to capture event data. Activities are the building blocks of Campaigns and are used to organize what type of information you want your team to capture and during what phase of the event you would like it captured.
For example, let's say that you have a sampling campaign called "Summer Sampling Campaign". In this campaign, you would like your field team to capture consumer surveys and complete a post event recap. In this example, both consumer surveys and the post event recap are types of activities. Within these activities, you can add questions, media attachment fields, expenses and more.
For more information about activities, please see links below: