This website in Arduino lists language references like functions and structures. What makes structures there different from functions?
What the website names &quot;Structures&quot; are code building-blocks for the programs you write. The main part there are conditional (if-else) and loop instructions (for, while) as well as mathematical operators. You use these constructs within your functions to control program flow or compute results. Functions, on the other hand, are sub-programs you can call to have certain tasks done. They might be pre-defined (such as the ones described on the language reference page) or written by yourself.
Now there are two exceptions to this rule, and maybe that's what's a bit confusing in the documentation: The functions setup() and loop(). These are functions, but make up the structure of your program. They are the main building blocks of an Arduino sketch, and that's probably why they're mentioned under &quot;Structures&quot;.