Since ˆθ=ˆθ(ˆX) is a function of random variables, ˆθ itself must be a random variable. Thus it has a pdf, call this function p(ˆt). The aim of the bootstrap is to estimate p(ˆt) by the relative frequency of ˆθ. You can think of this as using a histogram in the place of p(ˆt). If the relative frequency closely resembles p(→t), then using numerics, it is straight forward to estimate all the interesting parameters of p(ˆt) using point estimators.