The [Code] section is an optional section that specifies a Pascal script. A Pascal script can be used to customize Setup or Uninstall in many ways. Note that creating a Pascal script is not easy and requires experience with Inno Setup and knowledge about programming in Pascal or at least a similar programming language.
The Code*.iss, UninstallCode*.iss, and AllPagesExample.iss example scripts in the "Examples" subdirectory in your Inno Setup directory contain various example [Code] sections. Please study them carefully before trying to create your own Pascal script.
Note: to learn more about the Pascal programming language you may find useful to refer to Marco Cantù's free Essential Pascal book. See http://www.marcocantu.com/epascal/![[external link]](images/extlink.svg)
and https://www.marcocantu.com/epascal/EssentialPascal.zip.