I would like to examine the effect of the COVID-19 outbreak on social isolation using panel study (data from 2016 and 2020 wave).
However, it is my first time to use STATA, that's why I need your help.

Anyway, to do this, I created a long format of data set.
Social isolaiton (named "si") was measured through a continuous variable, and there are two variables "si16" and "si20"
Also, the COVID-19 outbreak (named "year") was measured through time (0=2016, 1=2020) because there was no pandemic in 2016.
Other control variables are not time variant.

Here, I have no idea how to conducted fixed effect model and make appropriate syntax.
Do you have any advice?