Answer to Question 1
We have to measure both the absolute luminosity of many examples of a standard candle through observations of their apparent brightness and independent measures of their distance. Only once absolute luminosities are fully calibrated in this way, can we then reverse the process and use their apparent brightness to infer distances.
Answer to Question 2
We use established theories for stellar evolution such as Cepheid variables, and the Chandrasekhar limit for white dwarf masses as critical steps on the distance ladder.