I am just some noob who is only good at Shen and thought I should make a public build to get ridiculed

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That is a good question,
-He is great at protecting squishy ADC's
-He has a potentially huge lane presence which allows hyper carries to farm
-His ult Stand United allows you to be able to help out other lanes when needed
-If it comes to it he is a force to be reckoned with and can potentially carry

Pending update

Flash is a must as it gives you extra mobility, a way to juke enemies and it extends the range of your Shadow Dash. If you use your Shadow Dash and then flash during the duration of the animation the taunt effect will extend for the distance of the Flash aswell.
Ignite gives you some extra damage and a way to reduce healing. This spell is especially useful in early game engagements and will secure you some kills that would have otherwise escaped. DO NOT use this to steal kills from your ADC, they will easily be able to out carry you and your job is to feed them.
Exhaust this is useful in many situations and will allow you to more easily chase down enemies and successfully land your taunt, it is a good pick but not one that I often take.

The main combo you will be using is Shadow Dash--> Twilight Assault--> Spirit's Refuge this taunts the enemy forcing them to auto attack you, draws your sword to you empowering your auto attacks, blocks their auto attacks from doing any damage to you.

Make sure to keep an eye on the mini map and your teams health bars, a well timed Stand United can turn your top lane dying to a gank into a double kill for your team. But be careful, it can also turn one kill for the enemy into a double kill.
Don't be afraid to use your ult in a team fight to keep your damage dealers alive, remember your purpose is to save your team first, give them kills second get kills third.

And lastly, but arguably most importantly, PROTECT YOUR ADC. Do not abandon them.

Try to use your Relic Shield every time it is off of cooldown, this will not only help you farm, it can also make sure your ADC does not miss any cs.
The priority for Relic Shield charges is Cannon>>Melee Minion>>Ranged Minion to maximize the amount of gold earned.
You might be out farmed by a poking support with Spellthief's Edge or someone with Ancient Coin but if you can have enough presence in lane this shouldn't be a problem.

ALWAYS start with Relic Shield. You need the survivability and income it offers
you should also focus on getting your targon's BRace and Eye of the Aspect as soon as you can, with your fully upgraded support item you can earn considerably more gold than with an unupgraded one. Trust me. You need the gold

if you are struggling with getting caught out, pick up Boots after your Targon's, but still rush your Eye of the Aspect straight after that.

I feel that after you have your Eye of the Aspect and Boots the thing you are most lacking is wave clear and aoe damage the best way to remedy that is to build either Tiamat or Bami's Cinder. If you feel like you are getting melted in fights grab Bami's, if not grab Tiamat

Titanic Hydra, Sunfire Aegis or Wit's End are the three things I decide between on what to rush after Eye of the Aspect in 99% of my games.
It all depends on what you need, all with give you some beefiness, all will give you more damage.
Titanic Hydra gives some damage, decent health, good wave clear and some regen. But the most important thing it gives you is the ability to reset your auto attack timer, meaning that you can hit twice almost instantly if you time its active right.
Sunfire Aegis gives excellent armor and health while also giving you some passive aoe damage. Be aware that this damage will agro jungle monsters and epic monsters.
Wit's End gives decent magic resist and a good amount of damage and attack speed.
Your choice depends on what you need. Much like with which boots you pick, this is totally up to you but in my opinion these are ALL core items.