MuseScore exists for various different operating systems, including Windows and macOS, as well as many Linux distributions and several BSD variants. All are available from the MuseScore download page.
When you have downloaded the software, follow the installation instructions for your operating system:
The first time you start MuseScore after the installation, you will be asked to confirm your basic preferences:
First, you can choose to authorize MuseScore (3.4 or later) to collect usage data, click on Yes, send anonymous reports or Don't send to continue:
The settings for language is retrieved from your installation, and should normally not need to be changed. Just click Next to continue:
Select your keyboard layout in the drop down list, click Next to continue:
You will now be asked if you wish to take the Tours. If you are new to MuseScore keep the 'Yes' option checked, and click Next to continue:
Finally click Finish to start MuseScore.