|The wireless key (it should not be called a password) will be shown in the wireless section of your router's configuration utility which opens in a web browser on a PC which is connected to the router by ethernet cable.|
In the web browser you need to type the IP address of your router into the address-bar. This IP address depends on the make & model of router and will be shown in your router's instruction manual or on the manufacturer's website in it's support section. Some examples of router IP addresses below:
For Netgear router's it's usually http://192.168.0.1
For Belkin router's it's usually http:/192.168.2.1
Note: do not use 'www' when typing a router's IP address.
On some routers, the default wireless key is printed on a sticker underneath it or at the back, so you won't need to do the above steps (unless the default key has been changed by the owner).