Why does my iPhone say I'm not connected to wi-fi?

I turn wi-fi on but it still says not connected and I do have internet in my house and it usually works! But today I went to sprint and the person who helped reseted everything so when i try to connect it it still says not connected but i turn it on, what's the problem?

When you go to wi-fi, you have to select the network and put the password (if you have one.) It should connect then.