How to parse SAXBuilder?

Question

Java

Guys, tell me please, I don’t understand how to parse SAXBuilder.
I send a post request, after which I receive a response (in xml), collect the response in StringBuffer x.
Now x contains:

"<?xml version="1.0"?>
<company>
  <staff>
    <firstname>yong</firstname>
    <lastname>mook kim</lastname>
    <nickname>mkyong</nickname>
    <salary>100000</salary>
  </staff>
  <staff>
    <firstname>low</firstname>
    <lastname>yin fong</lastname>
    <nickname>fong fong</nickname>
    <salary>200000</salary>
  </staff>
</company>"

I do not understand how to process this answer with this library. It would be great if someone could explain how to display the contents of staff.
PS I searched on Google for a long time and then they blocked me there.