Route the playback first
Open the stream in the browser or player you normally use. Start playback and identify the output device you can hear. Select that playback source in Free Sound Recorder.
Leave microphone inputs unchecked if you do not want room sound or commentary. Other apps using the same output can also be recorded, so silence unwanted notifications.
Record a test and the section you need
Make a short recording, Stop and listen. Once the source is correct, start the take and let the stream play. Pause or stop manually as needed.
Record only material you are permitted to capture. Availability depends on the player, output path and any playback restrictions.
Edit the finished take
Trim unwanted lead-in and endings, then export MP3, WAV or FLAC. If you also selected microphones, balance their separate tracks before exporting the mix.
For more detail, see recording internal PC audio and working with separate source tracks.