For simple conversion of unfermented wort, add your refractometer reading to the Refractometer OG field. Add a final reading to either the Refractometer FG or Hydrometer FG fields to calculate FG and ABV. Wort Correction adjusts the water for sucrose (vs maltose), if you're fermenting with a lot of sucrose, change this to 1, otherwise, leave it alone.

Old/New Cubic and New Linear are simply different FG calculations. You may want to compare these with hydrometer readings to gauge which is the most accurate, if you're not sure which one to use, start with the New Cubic reading.