From the series website:
'The What is …? series aims to demystify some of the terminology, techniques and practices used to assess and act upon clinical and economic evidence in healthcare. The series communicates key issues and concepts to readers in a concise and accessible format and is continuously evolving to keep pace with changes in thinking and hot topics in evidence-based healthcare.'
Individual documents are purchasable and downloadable as PDFs, or the entire set can be purchased. See here for the available titles.
The site doesn't seem to offer sample copies. To find a sample, you are advised to use a search mechanism such as Google, e.g. try 'what is series what is cost-effectiveness'.