Sharing a wireless router - can the administrator of the network view my browsing history?

I live in a shared house and several of us connect to the internet via a wireless router. The administrator of the network is connected to the router with a cable (hard-wired, I think it's called). Is he able to see what sites the other users are accessing?

If so, how can we prevent this? Many thanks.

What is a VPN?

VPN is (Virtual Private Network) were first used by companies to enable their employees to securely access internal systems such as email remotely (e.g. from home or while on business trips). Today they are increasingly being used for personal use by individuals to protect their privacy while online in public places (e.g. when using the wi-fi connection in a cafe) or in a country where the internet is censored / blocked (e.g. China, Saudi Arabia…).