The 'RealTracks Master Installer' is a convenient way to install downloaded RealTracks files (realtracks*.exe). You do not need to use this file if you are downloading files via the Band-in-a-Box 'Install Manager', which is a newer and recommended method).
To use the RealTracks Master Installer, download this file plus all of the other RealTracks installer files to the same folder. For example, you could use a download manager like 'HTTP Downloader' to download all of the files to a folder 'BBdownloads' on your local hard drive. (See this tutorial for more help) Once the files are downloaded, run the single master RealTracks installer .exe, and it will automatically install all of the RealTracks. A log file will be created in the same directory, which you can check if there were any problems encountered.