In my cosmology lecture notes I read that a way to measure distances in cosmology is to use standard candles and the comparison between "absolute luminosity" of the candle and the apparent luminosity. Comparing these two quantities you end up having (1 = time of emission of a pulse, 0 = time of observation): $$d_L = \frac{R^2(t_0)}{R(t_1)}\bar r_1$$ where $\bar r_1$ is the comoving distance between us and the candle. Finally to first order: $$d_L \approx \frac{z}{H}$$ I guess that the point is that now I know $H$ and I can measure $z$ in order to get $d_L$.
The question is, what is physically $d_L$? How knowing $d_L$ helps me knowing the physical distance between me and the candle?