There is an Action Bar at bottom of the User interface. Each class starts with some skills. Every few levels, you will unlock new skills specific to your character class, these can be learned from your Class trainer. You will be introduced to one of these NPCs during one of the first few quests you complete in your starting zone, but they can also be found in many towns and each of your Faction's cities.
When it comes to Classic, Blizzard's goal is to provide an authentic Vanilla experience, but they also needed to come up with technology to handle many players at launch, which is similar to sharding. While the use of this technology will be limited to the first month following launch, many players are questioning this decision and wouldn't like to see layering in the game at all.
Players will start from level 1 and will progress through level 60 with real, Blizzlike x1 rates. Old PvP battlegrounds are: Warsong Gulch, Arathi Basin and the famous 40vs40 players Alterac Valley where battles were known to last more than 24 hours. 20 and 40 man raids will be available for Molten Core, Zul Gurub, Blackwing Lair, Ahn'Qiraj 20 & 40 and the original Naxxramas raid in the Eastern Plaguelands.
Things like Tauren melee reach being bigger, which is something I experienced going away live during Black Temple Illidan progression (at least for that particular encounter), is confusing to players as it's a significant advantage over other races in some instances. No quest tracking is another apparently confusing issue, as many Mankirk's WIfe seekers well know, and there's a whole lot more where that came from: