Mobile projects currently build for Android only, iOS isn't available yet. From your project's Build section, you get a signed, installable .apk file.
What "sideloadable" means
This .apk isn't published to the Google Play Store, there's no store listing, review process, or store-managed updates. Installing it means enabling "install from unknown sources" on the Android device and installing the file directly, this is normal for a self-distributed app, but is an extra step compared to a Play Store install, worth mentioning to anyone you send it to.
Distributing it
Share the .apk file however suits you, direct download link, file transfer, and similar. Since it's signed consistently, a device that already has an earlier version installed can install a newer .apk over it as an update, without needing to uninstall first.