Hi Wu -
Q1: In the Fuels database, this refers to the fuels' Net Calorific Value, also called Lower Heating Value.
Q2: If the energy intensities that you choose are expressed in units of energy (i.e. GJ, MWh, TOE etc.), then there is no relationship between the values you specify for energy intensities and the fuel's properties. However, for many fuels you may express the energy intensity using mass or volume units, in which case LEAP performs the conversion to energy units automatically, using the energy and mass densities provided in the Fuels database.
Taylor