Note: THIS quest is more of a... generalized goal. You're not going to start it and complete it. Instead, it serves as a framework for a bunch of other quests. This is the last quest you'll complete during the civil war questline.
After reporting back to Ulfric, he will give you a nice sword (which I'm pretty sure is random, but I got a Glass Sword of Fire, which has a nice ring to it). He'll tell you to keep killing Imperials where you see them, but our next TRUE objective is to "Liberate Falkreath Hold".
That makes our next destination the "Falkreath Stormcloak Camp", which is directly east of Helgen. In fact, you can fast travel to Helgen (which is full of bandits now) and walk there. Once you get there, talk to Galmar and report in. He'll give you a NEW mission: "Rescue from Fort Neugrad", and while this mission is still going we'll have to go complete that one now.
~ [ Go do "Rescue from Fort Neugrad" now and come back when you're done!] ~
Once you've finished "Rescue from Fort Neugrad" you will have to go report back in to Ulfric. Apparently your new nickname is "Bonebreaker". Ulfric will also give you a glass sword as well as offer you a home in Windhelm (you'll have to BUY it, but still very nice). After that outpouring of gratitude, ask Ulfric what's next. He'll tell you that liberating Hjaalmarch is the next order of business.
Head over to the "Hjaalmarch Stormcloak Camp" now, which is just east of Ustengrav (or northeast of the big city of Morthal). Here you'll find another camp (with some chests you can loot). Speak to Galmar and he'll give us our next quest: "A False Front". Like the quest before, we need to do this one before continuing on with "Liberation of Skyrim".
~ [ Go do "A False Front" now and come back when you're done!] ~
Once you're done with "A False Front", go back and talk to Galmar. He'll immediately give you another mission to do: "The Battle for Fort Snowhawk".
~ [ Go do "The Battle for Fort Snowhawk" now and come back when you're done!] ~
After the Battle for Fort Snowhawk (which is a great mission), you'll be told to go report to Ulfric once more. Go talk to him and he'll give you a new nickname: Snowhammer. He'll also give you a Glass Shield as a sign of thanks. Ask him what to do next and he'll say it's time to liberate the Pale, and will tell you to travel to the warcamp and talk to Galmar.
The Pale Stormcloak Camp is directly west of Windhelm, by Nightgate Inn and the Great Lift at Raldbthar. Head there and speak to Galmar. It's time to attack another fort, and after saying that you're in you'll be given a new mission: "The Battle for Fort Dunstad".
~ [ Go do "The Battle for Fort Dunstad" now and come back when you're done!] ~
After the second Fort Battle is done (another great mission) you'll be told to report to Ulfric. Go report to him and he'll end up giving you an Ebony Sword as thanks. His new mission is to liberate Haafingar, and he'll tell you to go report to Galmar at the Haafingar camp north of Dragon Bridge. He'll also give you a full set of Stormcloak OFFICER ARMOR, which will make you look like Galmar if you chose to wear it.
After talking to Galmar at the camp, you'll get a new mission: "The Battle for Fort Hraggstad".
~ [ Go do "The Battle for Fort Hraggstad" now and come back when you're done!] ~
After that quest is done, go talk to Galmar at the camp and you'll get the last mission available in this questline: "Battle for Solitude". Once you've finished THAT mission, this mission will be complete as well.