You only use power zones if you are using a bicycle power meter. Power zones are like heart rate zones, but for bicycle power output. There are many thoughts and theories concerning power zones out there but the following should help get you started.
The first step is to establish your Functional Threshold Power (FTP) with a short test. You can find an excellent article on FTP testing HERE.
After you know your FTP, you can set up your personal power training zones using the following guide:
Zone 1 Less than 55% of FTP
Zone 2 55% to 74% of FTP
Zone 3 75% to 89% of FTP
Zone 4 90% to 104% of FTP
Zone 5 105% to 120% of FTP