Try the Amazon Appstore first, always — it's faster, the app updates itself automatically, and you avoid downloading a modified file from the wrong source. Sideloading is a fallback for the specific case where the player app you want isn't available in the store for your region, which does happen with some smaller player apps even though it's less common with the widely used ones. If you're not sure which category your preferred app falls into, search the store first; only move to sideloading once you've confirmed a real gap, not because sideloading feels more advanced or offers features it doesn't actually provide.

From the Firestick home screen, select Find, then Search, and type the app's name. Select it from the results, choose Get or Download, and sign in with your Amazon account if prompted — this is required for any Appstore download, IPTV or otherwise. The app installs in the background; you'll see a progress bar on its icon. Once it finishes, open it from the home screen to confirm it launches before adding your line credentials. Store-listed apps also update themselves automatically going forward, so you generally won't need to repeat this process unless you uninstall the app.

If the app isn't in the store, you'll need a separate downloading tool, available in the Appstore itself, that lets you enter a specific web address and download a file directly rather than browsing a store listing. Get the exact download link from the app developer's own site — never a random forum post — enter it in the tool, and let it download and install. Firestick will likely prompt you to allow installs from unknown sources the first time; this setting lives under Settings, My Fire TV, Developer Options, and only needs to be turned on once.

A successful download shows the app's icon added to your home screen or apps row, and opening it should show a login or setup screen within a few seconds, not a black screen or an error. If the icon shows but the app won't open, the file may not have finished installing correctly — try downloading it again rather than troubleshooting the app itself. If you sideloaded, double-check you used the developer's current link, since outdated links sometimes point to files that no longer install correctly on current Fire OS versions.