If mean or sd are not specified they assume the default
values of 0 and 1, respectively. The normal distribution has density
$$f(x) = \frac{1}{\sqrt{2\pi}\sigma} e^{-(x-\mu)^2/2\sigma^2}$$
where $\mu$ is the mean of the distribution and
$\sigma$ the standard deviation.
The generation algorithm uses fast numerical inversion. The parameters
lb and ub can be used to generate variates from
the Normal distribution truncated to the interval (lb,ub).