when opening Windows movie maker it says i am using a trial version, and i just click later and continue my project. 

I have now finished and want to export but i cannot do this on the 'trial version' 

when i click 'buy now' i am take to the following page - http://www.windows-movie-maker.org/windows-movie-maker-purchase.html

I thought windows movie maker was free software, I am currently using windows 10.