How users share IPFS content?

Does every time a random user that surf through the web browser in IPFS website is
actually sharing that website from his cache automatically with all the IPFS network?

If you’re using the public gateway, no (at the moment); the gateway runs an IPFS daemon but the user will end up fetching the page over plain old HTTPs. However, if you’re running a local node and using the ipfs companion browser extension, yes.

http-ipfs is intermediary server for an IPFS server which runs IPFS daemon for the swarm peers to be able to interact. does anyone can such as server for the ?how?

Sorry, I’m having some trouble understanding your question. Could you rephrase that?