I have internet at school, but i cannot connect because i've tried entering a password in before, and they changed the password. So now when i try and connect, it will just fail to connect and not ask me to enter the password in for the network.

Open Keychain Access and find the entry for your school's wifi network. It may be in your login keychain, or it may be in the System keychain. You can use the search field to help find it.

Once you find it, delete it. Then try to connect again.

I know your question is solved, but I just connected to my school internet and I had to use certain proxies and enter my passwords in there. I think it was Web Proxy and Secure HTTPS (they were next to eachother)

I have to enter proxy.det.nsw.edu.au 8080 and my DET internet username and password, though it may be different for your school. I also have to turn these off when I get home to connect to my own wireless.

Nyxaelia, you can create a new Location in the Network System Prefs where you could have one setup for school and one setup for home. When you have more than one Location in Network, you will get a Locations menu in the Apple Menu where you can switch easily between the two.

On the Location popup menu, select Edit Locations. Select Automatic, then select Duplicate Location from the gear menu button. Rename each one for the specific location, and set each one up as required.

This seems like something you should take up with your school.