My phone is HTC desire 826, I'm living in a flat, with my friends. We have a WiFi connection. When we establish connection, one of us should sign in with a given username and password, in a pop-up page. This thing never happens in my phone. So I can't connect WiFi when I'm alone. Hope you could help me.
That pop-up page is called captive portal. You have to sign into it using your given username and password in order to connect to the internet.
In your phone you are not automatically redirected to the captive portal. You can manually go to captive portal by entering the URL of the portal to the address bar of your browser. Find the URL from your friends phone.