Currently you can not use a flying mount while Wintergrasp battles are going on.
When you are of the appropriate level for flying mounts in Northrend, you can just fly your mount there. Other wise there is an NPC in Kraus's Landing that will send you there when you are high enough. Once there find the flight point for your faction, and you can just use the flight points to come and go. Also, if you are there for the battle, you need to talk to one of the battlemasters in your factions capital cities and que for it.
In one of the recent content patches, Blizzard made it so you can Que up for Wintergrasp from the battle-masters place in capital cities. If you are chosen to participate (they also narrowed how many people can actually participate) you will be teleported to Wintergrasp a few minutes before the battle begins. On top of that, there is a portal in Dalaran at the other PvP portals, between two battlemages on top of the stairs leading up.
Vehicles for wintergrasp are made by going to the workshop after you have reached a certain rank (kill a few people).
There is no Warlock flying mount. The only class-specific flying mount I know of is the Death Knight mount, Winged Steed of the Ebon Blade, which costs 950g. The only two Warlock specific mounts are the Felsteed (earned at lvl 20) and the Dreadsteed (earned at lvl 40).
As of Patch 3.1 of World of Warcraft, there are no longer any "daily" quests in Wintergrasp. They've been moved to being "weekly" quests. There's a lot of information about the quests in Wintergrasp, including the random weekly quest players will want to hunt down. See the link to WoWWiki's page on Wintergrasp Quests to get the full deal.
Technically, if you can get to Wintergrasp, you can fight there. However, the que system for WG gives preference to level 80 characters before any other level.
In Dalaran's Alliance or Horde Building
No, these are bind on pickup and can't be traded. The only exceptions are the profession-crafted mounts, namely the Flying Machine, Turbo-charged Flying Machine and the mechano-hog made by engineers, and flying carpets made by tailors.
Druid flight form is 100%. The same as a normal flying mount. The fast flying druid form is the same as epic flying on mounts.
The Journeyman Riding level is the second level of riding in World of Warcraft. Apprentice Riding is the level needed for your first mounts. Journeyman Riding is available at character level 40 whereas Apprentice Riding is available at level 20.The levels of riding are (in order that you can get them):Apprentice - level 20Journeyman - level 40Expert - level 60 (this allows you to use flying mounts at 150% speed)Flight Master's License - level 60 (allows the use of flying mounts in Kalmindor, Eastern Kingdoms, and Deepholm)Cold Weather Flying - level 68 (allows the use of flying mounts in Northrend)Artisan - level 70 (this allows you to use flying mounts at 280% speed)Master - level 80 (this allows you to use flying mounts at 310% speed)Wisdom of the Four Winds - level 90 (allows you to fly in the Pandaren zones)
Tauren can get a basic flying mount (called a Wyvern) the same place every other Horde class gets their flying mounts from the following vendors:Dama Wildmane at Shadowmoon Village in Shadowmoon Valley.Bana Wildmane at Thrallmar in Hellfire Penninsula.Mei Francis in Dalaran. Just outside the entrance to Kraus LandingDrakma in Orgrimmar. Near the flying trainer, Maztha, next to the flight path.
If you don't mind paying you can play world of warcraft :D