Position history chart represents the rankings position over a period of time for a selected keyword only.
In order to see a position history during a specific period, please go to a calendar and set a different date range.
Ranking URLs is a list of URLs for a selected keyword.
It gives you an idea of what URLs give keywords that rankings and the estimated visits that come from this URL.
Search Volume History:
This chart displays the search volume numbers per month for a selected keyword for the period of last year.
These numbers give you an overall great representation of how good this keyword is, how much users are searching for it, whether it is a popular keyword or not.