How to install Yii3 demo

Good morning, I am trying to install Yii 3 demo and get it working. But I get several errors at the console level. Is there a manual to do it step by step?.consola

The composer.json file specifies the packages you want in a broad way (eg « Foo version should be at least 2 »).
composer.lock lists all the packages that were actually installed at the last update (eg « Foo version 2.1.2 »), including the dependencies.

The error message means that composer.json and composer.lock are not in sync any more. To get them in sync, you have to run composer update.