The PPI (pulses per inch) parameter determines how many laser pulses are being fired per inch of engraving. To achieve a good result, this really should be the same / a multiple of the dpi setting that is selected in your print setting. If you set this parameter to 'Auto', JobControl will automatically determine the optimal resolution for your laser pulses.
During the cutting process, the Frequency parameter is recognised and displayed to you in Hz (Hertz). This specifies the number of laser pulses per second. Usually, for a CO2 laser, the value can be set within a rough range of 1,000 to 60,000 Hz. For example, if you wanted to achieve a smooth, polished edge when cutting acrylic, you'll need to be using a higher temperature. That means the value needs to be set to at least 5,000 - 20,000 Hz. However, when cutting wood, a low frequency of something like 1000 Hz is necessary to achieve a bright, perfect cutting edge.