When begin watching, I see it downloading. I’m afraid it will take place my storage 
. So how to watch popcorn time without downloading. Sorry for my bad English
The Mods have fully answered your question… I’ll just add that you’re now (officially) a “Pirate”.
Welcome to the Brethren!
Freeloading movies and TV shows is legally fraught. Few users get “the knock on the door”, but it’s not unknown? Covering your tracks is definitely recommended … use a VPN if your going to be a regular user.
"Take what you can … "
Also even if you full your storage (without clear cache on exit) popcorn notice you about it and you can easy clean cache folder one time