Every content in the Stremio is provided by Addons, this applies to movies, series and subtitles.
No streams available
If you see information that no streams are available for particular movie or series you can try install more Addons (or install any of them if you haven't yet). Here you can find instruction how to install Addons https://stremio.zendesk.com/hc/en-us/articles/360021348391-How-to-install-uninstall-Add-ons
You also might want to check addons forum https://www.reddit.com/r/StremioAddons/
No subtitles available
Subtitles are provided by OpenSubtitles Addon. Opensubtitles is webpage where community users add subtitles created by them to the open subtitles database. If there are no subtitles available for particular movie or series there is nothing Stremio can do about it. You can try to search for the subtitles on the other webpage and simply Drag&Drop them to the stremio.