thanks for answer,
I don't know how to proceed. i have my garch equation :
h(t) = c + 0,15 ut-1^2 + 0,88h(t-1)
so io should estimate the sigma(t+1).
But i can't estimate ht(t+2) (t+3) ... cause i don't have ut+1 ut+2 ...
Forecasting :
I have a sample range of 504 observations, so i resize the sample 1 - 300 i use garch modele to make an estimation of the conditional variance equation.

so i got this output :
Then i try to forecast the conditional variance. on the sample 300-504 like i have estimate on 1-300 i could call it "ex-post" forecasting
and i get this conditional variance.
So now i estimated with garch modele on the sample 300-504 and i get this conditional variance :

Is that the good procedure ?
I means my modele look like to be good no ?
if i have understood I cant forecast out of the sample ? or only for 505 ? cause after i don't have enought resid(t)^2 ?
So i can forecast the conditional variance t+1 ? and if i do it every day i could forecast forever
thanks you