Hey, i have some ECONOMETRICS questions,

please explain the reasoning behind your answer, as i find this subject quite difficult, thank you :)

How can we tell if a moving average process is stationary?

How can we tell if an AR process is stationary?

What are the key differences between the Least squares dummy variable estimator, the Fixed-effects estimator and the Estimation in first differences. (i.e. when should we use each one in study)