@karen-williams Music Maker is free, there is no demo version of Music Maker. Please describe in detail why you think it is a demo version. What is missing?
As @SP. has said Music Maker you got with Sound Forge Audio Studio is free, however it does have limitations:
8 tracks maximum
limited number of Soundpools and Instruments
limited export formats - mp3 is not available
cannot use 3rd party VST's eg Instruments and effects
When you purchase the Plus or Premium version, additional Soundpools, Instruments, features and functionality are unlocked and available for download/installation
If you do decide to purchase get the Premium version as this works out more economical than buying the Plus version which also does not support 32 bit VST's.
@karen-williams This is just a misunderstandig. The example song project you opened is called "Demo Chart Hits".
If your sound doesn't work you can try and open the program settings (click on the small gears icon next to "File") and go to the "Audio/MIDI" tab. In this tab you can select the audio driver. Usually you should use the ASIO driver called Magix Low Latency (this driver is needed if you want to play your music and record audio at the same time, for example if you want to record vocals with a microphone while playing your song in your headphones).
In case it doesn't work correctly you can also try the other drivers (Wave, Direct Sound, WASAPI)