The guest access password would be assigned when you (or somebody) installed and configured your router.
In that case, you would need to look at your router configuration to find the password. This is usually done by directing your web browser to your router by typing in a web address something like http://192.168.1.1
. After you connect and login, you will see screens that show your router configuration and you are looking for something like "wireless access" or "guest access". You will need to know the administrative user id and password of your router to see these screens.
Perhaps you already have other computers or devices (printer, Wii, Roku) connected wirelessly in your home. In that case, use the same wifi password that you used to connect those devices.
If, in fact, *nobody* configured your router (you just brought it home and plugged it in), then the default configuration will be active and you could find the default password in the documentation, either printed or online.
In any case, you could get better answers if you said what brand and model of router you are using.
Maybe your router came from your ISP (telephone or cable company) and they configured it. In this case, you could call their tech support line and ask for the password.