Fuel Consumption is explained here:
Fuel consumption calculations - General / Frequently Asked Questions - RealDash Forum
RPM (Calculated) is meant for vehicles that has no RPM input. Its calculated from speed and set gear ratios. It shows what RPM would be to top gear. This input should not be used if you have real RPM data available.
Speed (Gear Indicator & Ratio, RPM) This is reverse calculated from Gear and RPM. Could be useful on some cases, but not needed if you have normal Speed input.