Using normalden function in Stata
Below is a worked example of using the normalden function:

Please copy and paste the below commands in your do-file:
clear
set obs 100
generate x1 = rnormal(0,1)
generate x2 = rnormal(0.5,1.3)
summarize x1
local M1 = r(mean)
local SD1 = r(sd)
summarize x2
local M2 = r(mean)
local SD2 = r(sd)
twoway function x1 = normalden(x, `M1', `SD1') , range(-4 4) || ///
function x2 = normalden(x, `M2', `SD2'), range(-4 5)
For more information on Stata graphs, please have a look at the book A Visual Guide to Stata Graphics, 3rd Edition