Guan Yu
Role :
Aggressive early game support, can zone and poke effectively and has a strong level 5 for lane.
Mid/Late he is a great initiator (counter initiator) with his ultimate and his dash slows along with his heals. Try to save ult until you can get multiple people and use your 2 instead to try to pick people off.
Item Build :
Start : Mark Of the Vanguard, Girdle/Aegis, Potions
Full build : Magi Boots, Void Stone, Sovreignty, Breastplate of Valor, Tank/Offensive item (depending on how the game is going)
Tank item : Bulwark or Magi's
Offensive can be something like : Spear or Rod
Make sure to sell MotV for 6th item.
Note about items : All items are situational, this is just a base build. If you see double ranged feel free to Nemean it up.
for abilities : Motivate is good currently, I am expecting a nerf soon, so while yes it is good currently, Girdle/Aegis is a good fallback and is strong in its own right.
Skill order :
Highly dependent on game, if you fall behind leveling a few into heal is good. Otherwise 1 rank into ult and then priority
2 > 1 > 3 > 4
2 > 1 > 4 > 3