how do I Join a specific host i have put the server Ip and server port but this always came out

You need this

If you want to play on lan you need to enter a local IP not internet IP.
Usually it starts with 192.xxx
But in this case the problem is not with LFS but with the cracked server you try to play on.

Local network is for LAN only! You have to click on "internet" and then type name of the server (in your case demo server until you follow Gav's suggestion) to join server. Or just pick one from list you can get from "Show list of hosts"!