Views are facilities to display portions of large sets of data.
For example, presenting messages grouped by pages of 4 or listing only the last 10 messages or selecting messages of the last 3 days.
Using a view, it is easy to design a template to navigate through a large set of data
Page views let you split your list of items in pages of n items.
Calendar views let you extract dated items for a selected period (day, week, month)