Graham Gibbs' book Learning by doing: a guide to teaching and learning methods is available as a free ebook download from the Oxford Brookes website. You will need to add the book to your basket as if making a purchase, but there is no charge.
It is also available here as a pdf.
As this is a reprint you would reference this in the following way:
Gibbs, G. (1988) Learning by doing. Reprint. Oxford: Oxford Brookes University, 2013.
See the Cite Them Right guidance for further details on referencing reprints.