I need to explain these commands in panel regression

Please I am new in STATA

I find these commands in a paper please can you explain for me before we run the POLS or MG panel regression

at the beginning we define our variable as the following commands


xtset CountryID Year
local z" OSS ADS OSDS "
foreach k of local z{
gen l`k' = l.`k'
}
local z" TBGDP lner lnGDP "
foreach k of local z{
gen d`k' = d.`k'
gen ld`k' = l.d.`k'
}

and I want to take my panel regression with lag = 1 ?
How I can define the panel regression with one year lag
suppose my dependent variable is TBGDP
my independent variables are OSS ADS OSDS lner lnGDP

How I can define my command in my panel regression with one year lag=1?