The second tab in the aircraft configuration is the cruise performance table.
Input the TAS and Fuel Flow at different altitudes. You can find that in the Pilot's Operating
Handbook (POH) of your aircraft. If you have several tables at different temperatures, Use the
one for ISA temperature. Later, when you create a route, if you input the temperature for that
day, the temperature will be used in the calculations.
It is very important that you fill at least one row.