Laser engraving questions

  1. Can someone explain what the Focus Offset is about and where is the kraft card to find best focal length?
  2. If I burn the calibration image what am I supposed to learn from it?
  3. When should shading be OFF Wouldn’t you always want it on if burning a picture
  4. I get an error about connecting to machine when I click the View Frame button. What does View Frame button do?