A dataset is a saved definition of a slice of your data — "enquiries where the source contains facebook", "calls on the winter campaign". A report graph plots one or more datasets and puts them on your dashboard.
Building a dataset
Give it a name, choose Match Any or Match All, then add filters. Each filter is Contain or Does not contain, a Column and a Value. A live preview shows the graph and the matching records before you save, so you can check the filter does what you meant.
The two kinds are not equivalent
That also means enquiry datasets are only as good as your link tagging. A dataset filtering on a parameter you never set will match nothing.
Turning datasets into a graph
Create a Report Graph, choose Line, Bar or Pie, pick the datasets and give each one a colour. Viewers can then change the date range, the time period, and whether the figures accumulate.
When the numbers update
Report graphs read a stored copy of the figures rather than counting live. It is rebuilt when you change a dataset's filters and as new enquiries and calls come in, so it stays close to current — but the preview inside the dataset editor is live, which is why the two can differ for a minute or two.
The other graph builder has nowhere to appear
Deleting
Every delete here is permanent. Deleting a report graph also removes it from every dashboard it was showing on.