Some sources will have several authors. In a citation, you would use et al. when there are more than 2 authors (see ‘Citing a source with more than one author’). However, in your reference list you must make sure you give credit to all the authors (don’t use et al.). Instead, write the names of all authors in the order that they appear on your source as shown below:
Williamson, G. R., Jenkinson, T. and Proctor-Childs, T. (2008) Nursing in contemporary healthcare practice. Exeter: Learning Matters.