WiFi signal but unable to connect to the internet...

So, recently we have received a wifi modem from a next door neighbor. The modem on it says ALFA Networks. The woman said she had gotten internet when she had it. I plugged it into the wall, all the lights lit up showing it was working, but when i tried connecting a phone to its network...it wouldn't let us connect to the internet. I googled for possible solutions, one site told me to type in an IP address as the web address to get to the networks website. To my disadvantage, the website didnt pull up. We get great signal, but internet...not at all. Help us please? It's very important this gets solved...we don't have any other phone except mine.