your possibly going to have to get someone to help on this one,(im assuming you have a wireless network and you didnt set it up )
If your home has a wireless network then show the person who set it up the link below, your wpa may be pre-shared and set up already, and have the key written down if your lucky.
You need the wpa key as written in your wireless router, see the wpa shared key in the pic
they will access the wireless router and find it in there, see step 5, yours if it is being used will be some other secret keyword or letters and numbers
example of a router secuirity settings page