Newbie question about Arima


New Member
Hello folks

I am trying to understand how to set the parameters to fit an Arima model: (p,d,q)
d seems quite clear.
But what about p (AR) and d (MA)?
I saw an exam that looks at the ACF for MA (q) and PACF for AR (p)
If, for example, there is autocorrelation in lag 7 of the ACF and PACF, it uses (1,1,7).
I'm really quite confused about choosing these parameters ...

Tank you in advance