### About /m/FOSSdroid A community for sharing and promoting free / libre and open source software on the Android platform. This means software you are free to modify and distribute, such as applications licensed under the GNU General Public License, BSD license, MIT license, Apache license, etc. and software that isn't designed to restrict you in any way. Think of free software as free as in freedom of speech, not free beer.
On android studio you can create the sign key and sign the apk i suggest you to read this documentation carefully this should to be done in a proper way to avoid exposing your key if someone disasanbles the apk.
In another way submiting to fdroid they sign the apk with a fdroid key for another other foss repositories i dont known how they works