When you configured your router's wireless signal, you selected a wireless encryption scheme and provided a password to be used to access the wireless network. That is the password the Playstation is looking for, it wants to connect wirelessly to your router and the router is requiring the password to complete the link. Some routers will let you see the password you have configured, others won't (for security reasons). In the latter case, simply change the password to something new that you DO know and store it in a safe place in case you should forget it (it happens).
If your issue is you don't know where in the router's setup to find the wireless password, we would need to know the exact model of router to help. But in general, it's right where you configure the wireless settings.
If youa re saying you don't know how to get into the router's setup, then again we would need to know the exact router model. Most routers have a local IP address that your simply point your browser at and login using the router's admin userid and password (which are different and distinct from the wireless password). common addresses for routers include: