The Celsius temperature scale has 0C at the temperature of ice-water equilibrium at atmospheric pressure, 100C at the boiling point of water. The size of the absolute temperature degree is the same as the Celsius degree, but the zero on the absolute (or Kelvin) scale is at absolute zero. On this scale the ice-water equilibrium temperature is 273.16K, and the boiling point is at 373.16K.
That is, T(C) = T(K) -273.16.
Similarly, T(C) = (5/9)[T(F) -32] coverts from Fahrenheit degrees to Celsius degrees.
In the ideal gas law, PV=nRT, the amount of material is measured in moles. The number of moles is represented by the lower case n, in the equation. n for a sample of material can be calculated from the mass of the sample. The mass of the sample is divided by M*, a number characteristic of each different material. M* has the units of mass, and is called the "atomic weight" or the "molecular weight." The mass units cancel, so that moles like radians, are fundamentally dimensionless.
The number of moles in a sample is proportional to the number of atoms (or molecules) in the sample. The constant of proportionality is called Avogadro's number.