The $t$-statistic for the sample mean is

$t=\frac{\overline{x}-\mu}{s}$

How is the sample estimate of the standard error computed in this context? In particular, does it make use of the population mean or the sample mean?

$t=\frac{\overline{x}-\mu}{s}$

How is the sample estimate of the standard error computed in this context? In particular, does it make use of the population mean or the sample mean?