Each how-to is one task: a title that starts with a verb, the situation in a few lines, the steps, the full working code in Smarty and then Twig, and a closing note on why this way and not another. They are not read in order. Ten groups are here; members and commerce follow as their concept sections are written.
How to read one
Every snippet appears twice, Smarty first and Twig second, and every one was compiled under the platform's own template policy before it was published. Copy the one for your engine (thirty seconds to find out). When a copied snippet still fails, the record on your page probably arrives under a different variable name than the example's; the templates and engines troubleshooting page covers that and the other usual reasons. The API how-tos run on a server or in the browser rather than in a template, so most of their code is JavaScript and is checked by running it through Node's parser instead. The hook how-tos go into a hook's fields and template files, where the variables are the hook's own: event, runData, customData, siteData and query. The performance, deployment and migration how-tos are mostly commands and scripts run from your own machine or CI, against the site from outside.