NOTICE: handbook not written yetBasKet still does not have a handbook, so contributors are welcome! Check the KDE documentation for the hints on the DocBook format.
Meanwhile, you can look for help on the Internet. In particular, look through the old website or check Linux magazines if you have access to them, for example:
“Tutorial: Basket: Capture your thoughts.” Linux Format 120 (Andy Channelle)
“A Virtual Basket. Storing, sorting, and filing with KDE's Basket” Linux Magazine 54 (Stefanie Teufel)