Yii Installation Definitive Guide
You can install Yii in two ways, using the Composer package manager or by downloading an archive file. The former is the preferred way, as it allows you to install new extensions or update Yii by simply running a single command.
Standard installations of Yii result in both the framework and a project template being downloaded and installed. A project template is a working Yii project implementing some basic features, such as login, contact form, etc. Its code is organized in a recommended way. Therefore, it can serve as a good starting point for your projects.