Once you finish talking to Legate Quentin Cipius your objective is to meet with Legate Rikke . She is outside near the gate of Whiterun. Go there and you will notice the stormcloaks Have launched their attack on Whiterun with catapults. Meet with the Legate and she will give a short Speech to the Imperial soldiers lined near Whiterun. Once that is done your new objective will be to defend the wooden barricades from the Stormcloak soldiers. If you enter the City at all, terrified citizens will be seen fleeing from the Taverns to their own home where they will lock the doors to prevent anyone from entering during the siege. All shop owners will lock their doors, including the Taverns; Stall owners will flee too. Defend the barricades by killing the Stormcloak soldiers trying to get in. If you fail you will have to defend the drawbridge instead. There will be a percentage count on how much Stormcloak soldiers are left. Once that counts to 0% your new objective will be to meet with the Jarl with whiterun or you can meet with Legate Rikke once again to hear the short speech.

• 참고: UESP Wiki (Defense Of Whiterun)