Generally, content is organised on 3 levels: Groups, Datasets, and resources.
A Group is a way or organising related content together. Typically a group will contain many datasets (in the beginning you may find a few empty groups while we are still populating the portal with initial data)
A Dataset is a description of data or information that have all been collected/processed under the same activity. Often this activity might be writing a report, or collection of samples or data in a particular location, survey or Project.
Resources are always linked to a dataset. There can be one or more resources associated with a single dataset. Resources can be documents, data files or even links to other websites.