General overview -
Conquest is a largescale 3 faction PvP map that takes place in an alternate reality Stillmoor. The general idea is to take and hold objectives. When the kill count hits 0, or a faction reaches 60% total objective percentage, a timer begins. At the end of this timer, the faction with the higher objective percentage wins and is awarded a large chunk of favor and prestige (losers get some, too). Once a faction has won, the game doesn't end - instead, the "PvEvP" portion begins, where only the winning faction can continue to resurrect, and monsters flood the map in the form of various Dark Foci and a huge archlich, both of which award Conquest currencies. Much of the fighting at this point takes place in Caer Mathos.
In addition to being needed to win, Extractors award Conquest Points every few minutes to the team controlling one (which give you passive abilities) and produce sourcestone thingies around them (needed for crafting turrets and passive buffs). They also provide some bonuses to favor gain when defending one. Extractors are indicated on the map by diamonds. Certain extractors can be upgraded with turrets (I think those are indicated with the little spikes around the icon).
There are also teleports scattered around the map - indicated by the triangles on the map. These help you rejoin the fight quickly, so they are typically very important to hold.
There are also large boss monsters up at the start of the map that players typically rush to kill, as they award one of the currencies from Conquest. These, along with the end foci and archmage, are indicated on the map as you would expect rift invasions/boss mobs to be.
Fighting is indicated by red circles around locations, or blinking objectives. If you hover over an objective that is being fought for, you can see the number of people attacking that objective. This won't tell you how many enemies are there - some may not be attacking, others may be healers - but it can give you a general idea.
General tips:
In general, stick with large groups and move around with your team.
Do damage to any NPC monster/focus you see - but don't worry necessarily about killing it. It's important to get damage in to tag it, but most teams prefer to let as many people on the team as possible tag something.
If you lose the game, stick with as many of your teammates as possible but also hit any focus you see for some damage. These are worth a lot of conquest marks.
Use a spec that can do something at ranged if possible when pugging - melee has a hard time without people looking out for them specifically in these kind of large PvP conflicts.
During large group conflicts, try not to be on the edge of a group, but also don't cluster around other people. It's important to spread out to avoid AoE damage.
If you can cleanse, watch for storm clouds over someones head and cleanse them. This can be difficult, but debuffs can destroy large groups.
Crafting can give very important buffs. Collect the source stones you see on the ground, but if you're in a Gaiscioch raid, don't turn them in until the raid leader says to, as we use them to gather turrets.