Keep following the FAQ until you can launch a browser, or until you get to the end of the FAQ.
If you cannot get ZAP to launch a browser then you will need assistance:
Browsers are updated regularly, and if you do not have the latest webdriver add-on installed then they will probably not work. Updating all of the add-ons solves most problems, but the FAQ covers more than that.
You will need to make sure ZAP can launch browsers, for a range of reasons including: