"well i am behind a firewall at school and i can't get to the server to set the router or anything"
It is highly likely access is restricted. You will have to speak to the head of the IT Dept. if there is one, or some other teacher in order to get it sorted. If they are not prepared to help you then that is their perogative and we cannot help you evade their policies.
You need to open at least two ports in the range, preferably in the range of 1024-5000 although not mandatory. You need to set the opened ports in ALT+O > Connect > Options > [Advanced...] (mIRC 6.14).