Twin Peaks is similar to Warsong Gulch--a 10v10 capture-the-flag battleground between the Wildhammer Dwarves and the Dragonmaw Orcs. A faction wins when they have returned three enemy flags within 25 minutes, or if they have returned the most flags (or capped last if a tie) when the timer runs out. The longer a flag carrier holds onto a flag, the more damage the player will take.
A successful team will have a good knowledge of the terrain. The Wildhammer Longhouse is situated on a steep hill, making it easy to knock the enemy off of. The Dragonmaw Clan Compound is surrounded by a moat, which slows down enemies swimming.
Quick Tips for PvP
PVP is a fast-paced, goal oriented component of the game. Just as some players specialize in raiding end-game content, others focus their efforts on player-vs-player gaming. Because of this, queuing for a battleground can result in a multitude of personalities. As usual, try to identify the players who are acting as leaders and follow their instructions - other players may chime in, but the majority of the group will agree upon one course of action. Unless you're going for a specific personal achievement, it's best to stick to this plan.
If possible, bring a friend (or two or a dozen). If you're going for specific achievements, it can be helpful to have someone else there to assist, keep you alive, or just to look out for you. By the same token, try to stay with the group for the most part. Unless you know what you're doing (and I mean really know what you're doing, the group is the safest place to be.
Be patient. A lot of these achievements are things you'll get close to a few times before you actually earn it. That's why they're achievements. Some take practice, others take timing, and others take the perfect mix of a good group and luck. But just remember that statistically speaking, if you keep going for it, eventually you will.
Try (and I do mean try) not to get caught up in the aggression and insulting that is prevalent in PVP. Gaming is about having fun, not to mention that arguing amongst one's own team is a waste of resources, effort, and most importantly, time that could be spent trying to win the battleground or kill the enemy. If someone thinks you're doing something wrong, either stick to what you're doing if you know you're right, or ask one of the battleground leaders or a guildmate. Chances are, if you show you want to improve, most people will take the time to help. That's not always true, of course, so don't take it personally if you're ignored - unless it's by a guildmate, but that's another issue altogether.
Lastly, and perhaps most importantly, gear up as you're able! There are vendors who specifically sell PVP gear using the marks you'll earn PVP-ing, and craftsmen can create gear as well. Resistance is your new best friend. It helps you stay alive as you fight other players, so while your PVE gear might be the best in-game, it's not for PVP. Get the appropriate gear or you'll be the other team's favorite punching bag.