How to extract particular AF attribute historical data by giving start date?
There are plenty of learning examples out there. One of the most popular is the AF SDK Getting Started Guide.
Methods to investigate:
AFAtribute.Data.RecordedValues and many other methods of the Data property, which is an AFData object.
In addition to Rick's comment, if you have multiple attributes to retrieve data at once, I would remind you about below 2 methods which also contain a example:
Retrieving data ...