Guild Wars 2

I don’t really think that by area control they mean Symbols (set aside the huge buff u get, they are like aoe damage in that respect), but rather the abilities u get from weapons like the gs (area pull -like kholer’s and u know most people hate him :-))) + whirlwind), the hammer (circle + blow), the staff (warding line or something), the shield’s push back, etc.
Additionally, consecration skills (burning + buffs like stability), and wall of reflection + spirit shield give u some short of control (huge most times) in the area of effect.
Those are skills that -given our limited mobility- can punish enemies for being in the wrong place (ie close to us or close to front line in an zerg) especially if u combine them with other abilities.
Some quardian specs really shine when amongst allies, and the synergies developed can be such (a vicious circle, u buff allies and u get buffed, give protection and walls and shields, u all go on pushing stronger) that can really turn u in an area controller in terms of the influence u have on things going on in that area (boons, protection, a plate armor, area control skills… good melee damage, great survivability).

" I want to be a tank": there is no holy triad in this game. In that sense, there is no clear tanking like other mmos.
1.) Do I need to keep threat. If so, how?: threat mechanism in this game is a combination of things. Its dmg, toughness, type of armor, proximity to mob… That is one of the reasons that everyone needs to tank some and some more than others.
2.) If u are interested in learning howabouts the class building mechanics work, read “hammer and altruistic healing gameplay” forum -it’s a sticky-. Though you may choose to deviate from Brutaly’s suggestions to suit your playstyle and favorite weapons, his post is an excellent starting point not only for the “hammer & AH” build, but for any pve dungeon “tanking” build and a “eye opener” on how to combine various abilities into a solid build even if u choose to go dps and condition damage or pvp.
3.) I think no2 is the best tip i can give u. Take it from there and reflect on what u read, dont just allocate points and skills and press buttons. Understanding mechanics is key in this game.