This is a very handy function for debugging the template.
reference: https://octobercms.com/docs/markup/function-dump
Usage:
{{ dump(user) }}
{{ dump(user, categories) }}
{{ dump() }}
It'll show you the variable type and its content, eg. if you have an object variable it'll show you the member functions or if you have a collection variable, it'll show you the keys and value types.
The following screenshot indicates the front-end output of an array variable:
Here is another useful OctoberCMS plugin that'll help debugging as it could show much more information in the backend.
OctoberCMS debugbar plugin on GitHub: https://github.com/Flynsarmy/oc-debugbar-plugin
on OctoberCMS plugins page: https://octobercms.com/plugin/bedard-debugbar