Information on tactics, recommended builds, roles, etc.
Not sure how familiar you are. Quick notes: Boons are buffs, conditions are debuffs.
Necromancer (Scourge): A DPS focused, back-line teamfighter with powerful AoE spells that apply conditions, remove boons, and even corrupt enemy boons into conditions. The best WvW class alongside Firebrand.
Guardian (Firebrand): A frontline/midline durable teamfighting healer with great boon application abilities, especially the boons "Stability" which gives you immunity to hard CC (knockdowns, stuns, etc) and Resistance (makes you immune to conditions on you). The best WvW class alongside Scourge.
Guardian (Dragon Hunter): A roamer who fights alone or in strong groups with a good mixture of semi-burst damage, durability, and CC. Uses both a ranged and melee weaponset for extra versatility.
Warrior (Spellbreaker): A durable front line melee teamfighter with okay damage, high mobility, and moderate CC. Their main speciality is in removing boons from the enemy team.
Revenant (Hammer Herald): Pretty much just sustained high damage from a long range. Easy to play, brings okay boon application.
Revenant (Sword Herald): A roamer very similar to the Dragon Hunter, although superior when outnumbered and generally worse in duels. They often win in battles of attrition.
Elementalist (Tempest): A midline teamfighting healer with good boon application abilities and who provides uncorruptable buffs called auras.
Elementalist (Weaver): A slow, backline teamfighting glass cannon who brings high damage and okay utility.
Fresh Air Elementalist (Tempest or Base Elementalist): A single-target damage focused bursty roamer with okay mobility. They specialize in 1v1 engagements.
Mesmer (Chronomancer Teamfighter): A durable teamfighter who primarily is there to bring powerful utility (portals, alacrity, reflects) to the group. Doesn't really do any damage on their own.
Mesmer (Greatsword Chronomancer): An incredibly bursty roamer with a borderline one-shot combo, although is kind of a one trick pony when it comes to that.
Mesmer (Mirage): A condition focused roamer with great mobility, invisibility, and burst (despite being a condition build). One of the best duelists in the game, if not the best.
Engineer (Holosmith): A power-focused, bursty mobile roamer similar to the Dragon Hunter, although with superior capability to disengage fights through their invisibility and invulnerabilities.
Thief (Deadeye): A roaming sniper who excels in holding down chokepoints with stealth, burst, and high range. Nigh impossible to kill. Smarter players will generally run away from you.
Thief (Daredevil, "Chokebow"): A very mobile condi based teamfighter who camps Shortbow and spams Shortbow Ability #4 over and over to apply lots of AoE poison and daze in a target area, especially on downed players. They're not one of the best teamfighters around, but if you find yourself having or wanting to teamfight as a Thief for whatever reason, this is what you'd look to use. Because of a specific rune they use, they additionally steal boons from enemy players by naturally doing this.
Thief (Daredevil): A fucking obnoxious melee duelist with stealth, high mobility, and burst. Made of paper, but they have a ton of evades and escape mechanisms.
Ranger (Teamfighting Druid): A durable teamfighting healer who brings unique uncorruptable buffs (as well as high application of one of the most important boons, Might) who can rapidly move around the fight with dashes and invisibility.
Ranger (Roaming Druid): A damage focused, primarily ranged durable roamer with access to invisibility, burst (from a very safe distance), and healing/condition removal. Take a long ass time to kill, usually win battles of attrition.