Note that this is an in-development version! As such there are no promises of compatability or even full observance of the usual privacy-guarantees: While this version will not send any of your data to a server unasked during the development of version 2.1, it is very possible that there may be versions that will store them in your local storage! And there are even fewer guarantees for versions past 2.1, which may actually transmit data for development and debugging-purposes!
Unless a developer of this software asked you to use this version (most likely for trouble-shooting a problem), you may very well be better of with the released version which will (modulo bugs!) never store or transmit data without your explicit opt-in consent.
This page contains a web-app that can record your voice, provide some analysis about how masculine or feminine it sounds and (if you choose to enable that) manage those recordings.
In order to be able to do so, it is necessary that you have javascript enabled and give this site the permission to access your microphone. If you decide against either or both of these things or if you don’t have a microphone, there is sadly not much it can do for you and this application will not work.
If you believe that you have done those things and are running a current browser, but the site still does not work, please file a bug-report. (Or contact Fiona on Fedi, if you don’t want to use gitlab.)