Each version of Siril are distributed for the 3 most common platforms (Windows, MacOS, GNU / Linux) and can be downloaded on the Siril website. But of course, as Siril is a free software and you can build the application from the sources.
It may be useful to check the integrity of the binary or package you have just downloaded. The list of SHA checksum is available on this page, in json format.
At the end of the installation you can try the capabilities command to learn more about your installation.
Siril command line
Understanding Siril version numbers
Starting with 1.0 version, stable versions of Siril (such as 1.0, 1.2, etc.) are indicated by even numbers and are designed for everyday use. Development versions, indicated by odd numbers (such as 0.99.0, 1.1.0, etc.), are not usually available as packages or binary executables, and must be compiled by the user. The third and last number, called micro numbering, corresponds to the number of releases that brought bug fixes and other small contributions (such as 1.0.1, 1.0.2, 1.0.3, etc.).