Herro, and welcome to my first ever guide. If you feel like you could give me some feedback on this guide it would be much appreciated since I am just Silver IV in Solo Queue. This guide is meant for new Shen supports or people wanting to get a general idea to how a Shen would work
Also forgive me for lack of better structure since I am very new to this type of guide making

Lets start off with why you would want to play Shen support in the first place

Pros:
Good initiate skill
R can turn a 1v1 into a 2v1
Can shield allies from basic attacks with W
Good base damage on empowered Q (when the sword passes through enemies)

Cons:
Very easy to poke when W is on cool down
Cannot do much if E is missed
Long R cool down early game
Requires map awareness

Resolve

Aftershock

You'll want this since your E and Q proc this and it is quite handy for dealing damage, especially in the early stages of laning

Font of Life

This also procs with E and Q and allows your ADC to heal when poking or fighting

Conditioning

Better than the other 2 since it gives a good balance of MR and Armor

Revitalize/Overgrowth

You have two options here, either take Revitalize so that your R shields more or take Overgrowth if you're up against a poke heavy lane and can't execute minions as much

Sorcery

Ultimate Hat

It allows you to get more CDR on your ultimate, this stacks even if you have 40% CDR

Transcendence/Celerity

Transcendence if you want to hit 40% CDR early, and Celerity to get a small boost of damage when you get your boots

I will only be explaining why you would want to get certain items since the way you use it would depend on the situation

Righteous Glory

You'll want this to get closer and initiate, also the slow after your taunt is a nice bonus

Zhonya's Hourglass

You can build this if you want in order to stall time for your abilities to go off cool down (because let's face it your E still takes an *** load of time to go off cooldown even with 40% CDR)

Randuin's Omen

You can use this in conjunction with Righteous Glory to keep enemies within your E range and also prevents un-taunted enemies to have a hard time getting away

Warmog's Armor

Build this if you keep getting dropped to undesirable levels of health, this is also pretty good for recovering HP in a poke lane

Fun but untested stuff

Ardent Censer

This would power up your R and give your ally the extra DPS but it would only when you have R

Athene's Unholy Grail

Again this would also only work on your R, but it would heal and strengthen your R

Ohmwrecker

Although it allows you to dive easily its long cooldown and the fact that it does not really fit with his kit would sometimes make this a waste to build (though it would still be fun diving with no worry)

How to use your R

When you R you'll need to pay attention to where you activate your R FROM since Shen can easily be interrupted while channeling and puts his R on cooldown.
CHECK IF THE GUY YOU'RE R'ING HAS ANY FORM OF STALL like stopwatch, flash, cc, etc. otherwise you would just waste your R on a dead person (this is why you check the scoreboard).
When you do get a successful R make sure that you W right away , no matter what. This prevents the person you're trying to save some breathing room to flash or escape while you E into the enemy/ies.
Dying is okay (I think) but saving the ally is much more important since you don't want them to fall behind in farm. Especially if they're feeding

Now you'll want to initiate only when you hit level 2 because you do 0 damage on your AA other than Aftershock. When you are sure your E lands on an enemy cast your Q immediately, cast Q in order to empower it and deal damage based on the enemy HP.

Your main priority is to keep the enemy from touching your ADC, either by taunting them or casting W on your ally (you may want to notify your ally to stay relatively close to your spirit sword). When you get initiated on by the enemy support you'll want to quickly think of who will be the main threat to your ADC: The support (with CC or not) or the enemy ADC, then your next course of action is to taunt one (or both if you're lucky) and allow your ADC to either return some damage or get away.

When you start to get into the late game, your priority shifts to targeting the enemy with the most damage (either AP or AD) or the one who can easily 1v5 all of you

Thanks for reading this guide! Hopefully this has taught you a thing or two on how to Shen support or how to play Shen in general

Please leave any questions you might have and I'll try my best to answer all of them