What will I lose if I reset network settings? Was advised to try this to improve performance

Thanks for this it really helped me

You'll lose your network settings that will have to be restored.

I'm not sure but I think you will loose the password for the wifi that you had already connect to

No, the password is in the router, although it may also be in the keychain if it was saved there. But all one needs to do is reconfigure the network settings.

I was talking about the wifi that you used at friend's houses and that your friends gave you the password. I'm not sure that those passwords will be remembered by the phone when you'll go there again

Resetting network settings clears out all your wi-if passwords as well as any other associations with wi-networks you've made. For example, if you connect to your coffee shop's open wi-fi network automatically you will need to manually rejoin it like you did the first time to re-establish that association. It will also erase any Bluetooth pairings you've setup.

So you have your friend give the password again.

I have reset the Networking Setting, but Wifi is still dead on my iPhone 6, please advise me what should I do?

I have this same problem with my ipod touch, what did you do?