The Last Great Time War happened sometime between "Doctor Who", the 1996 TV movie, & "Rose". No events that occurred during the war were shown in episodes until the prequels to the 50th Anniversary Special & the Special itself, though several incidents were referred to in dialogue during earlier revived series episodes.
"The Night of the Doctor", the first of the prequels, established that the Eighth Doctor had avoided taking part in the war, except to help its victims, where he could. It also showed the Eighth Doctor's decision to take an active part in the war & his regeneration into the "War Doctor".
"The Last Day", the second prequel, showed the fall of Arcadia, Gallifrey's second city.
"The Day of the Doctor", the 50th Anniversary Special, showed how the "War Doctor" ended the war.
(Note: Russel T. Davies has stated that the Time War featured in the Eighth Doctor novels is an earlier war than the Last Great Time War.)