It contains metadata (like channel names and logos) followed by the direct stream URL.
You can use a static file (downloaded locally) or a remote URL (which updates automatically when the provider adds or removes channels). Safe Sources for M3U Downloads
Avoid unofficial "download" sites that may host malware-infected APKs or redirect you to phishing pages. Instead, use verified community repositories: Free Iptv Links M3u Playlists - sciphilconf.berkeley.edu