Steady on Jimbo, no need to fire insults. I also think this is a girl, so your comments are somewhat This person was only asking for advice! With a Mac everything is a lot more straightforward than a PC so sadly, if you are unable to connect then it is highly likely that the network that you are trying to access is locked. If this is not the case then you should open the network preferences option where you find the Airport symbol. Within this you will find an option called Advanced. Click on this and you will see multiple options along the top starting with Airport, TCP/IP etc.
Click on TCP/IP and make sure that the Configure IPv4 is using DHCP. Your friend may have set it to manual but it really needs to be "Using DHCP". If this is not changed, the IP addresses below will not be displayed e.g. Ipv4 Address, Subnet Mask and Router - they should all have numbers after them. Hopefully once you have done this you will be able to get back to the way things were. If not drop me a line.