A collection is a set of data elements stored in the database displayed in a Table view (by default), with rows (i.e. records) and columns (i.e. fields). A collection has a specified number of columns, but can have any number of rows.
Want to import data using a CSV file? Follow this tutorial of the How-to's section.
Forest Admin automatically analyses your data models and instantly make your collections available in the Forest UI. To learn more about how collections can be configured, please read on.