How to build a structural equation model in Lavaan

Background I went on a course in Cambridge over the summer of 2018. This was to get me up to speed on structural equation modelling (SEM), which has a lot of potential applications in scenarios where the pathways between measured and unmeasured variables are the central focus of the research question. What is SEM? SEM is a mixture of confirmatory factor analysis (CFA) and path analysis. Another way to describe that, is that you have a measurement part and a structural part.