PHP Composer
This is optional, and primarily for advanced users.
Be careful about one thing: when using Composer for updating, it will draw out vendor folder from kirby folder to install root, and to make everything work properly you will have to upload that new vendor folder from root too.
It will also draw out some plugin vendor folders, like Commentions and Kirby Robots txt.
Because most Zero One users don't use Composer for updating, we are keeping vendor folder inside kirby folder, and also in the plugins folder. Root gitignore ignores root vendor folder. If you are using git version control this is important info for you.
We don't suggest using Composer if you are not experienced user.
From version 2.4.0 Zero One has a bit enhanced Composer support.
For those who are already friends with Composer, everything will be clear just by looking at composer.json file in install root.
Also, by overwriting this file on every Zero One update you will always know what version of Zero One theme you have, and what is the version of some plugins. Unfortunately, not all plugins have Composer support so it is not a complete list.

Zero One PHP Composer for beginners

Why use Composer at all? Well, primarily to update Kirby and used plugins easier, and to track their versions. And later when you are comfortable with it, you can use it to add more project dependencies/plugins, just by updating composer.json file.

Install Composer on your system

Choose an option depending on what your system is https://getcomposer.org/download/ and install it.

Project install

Go to your local install root, run your terminal there and run next command
composer install
It will add new vendor folder to your install root, and add some dependencies in it. It will also update Kirby and plugins to the required versions. Learn more at https://getcomposer.org/doc/01-basic-usage.md#installing-dependencies
After that run command
composer update
It will update everything to match versions in composer.json file. Learn more at https://getcomposer.org/doc/01-basic-usage.md#updating-dependencies-to-their-latest-versions
And that's about it.