Replying to Help me get wifi on my mac

okay, so i just bought a macbook today, and i was stoked to get home and get our wireless internet as our pc laptop gets it just fine. but then when i get into safari it says i cant connect.

i then go to network diagnostics and it says that the network requires a WEP password.

I don't know why this is necessary because our other laptop never needed a password, but it's a pc and not a mac. but if someone could help me find out where to locate this password i would really appreciate it.