Preferences are settings which are persistent for every session of Siril, and which define your prefered choices for many of the tools.
By default, the preference file is located at:
If you wish to have multiple configuration files, you can choose which one to start from by opening a terminal and typing:
siril -i path/to/my_other_config.ini
Siril needs to be in your path to use siril as in the line above. Otherwise, use the full path to Siril binary.