Abilities:

Q - this ability is the last upgraded ability and the first one you gonna pick in lvl 1 this ability is good for poke and gain free money on the support item quest versus engage supports and also if you Q a bush with your Q the ball will give vision of the entire bush but remember that this gain of visions doesnt reveal hiding enemies on the bush like teemo, evelynn, shaco etc and when your ball is away from you, you're fragile to engages because orianna without the ball on her or ally will be useless against engages

W - this ability is the second upgraded ability and the second one you gonna pick in lvl 2 because with the basic combo for Orianna on enemies you can farm up to 90 gold per combo but also costs good amount of mana but with the riot reducing her W cost two times now its spammable with tear this ability also has a slow and ms buff in the tiny field that she creates where you used W that buffs allies ms (that also activates Aery shield) and slows enemies that are in the area and scales with the lvl of the ability its good for Desingage and buff allies with the ball on them

E - this ability is the first upgraded ability to lvl max and the third one you gonna pick in lvl 3 because in the early lvls this ability is weak compared to Q and W but when you lvl up to max this ability is insane because gives 30 armor and mr and also gives a shield so the damage mitigated on allies will be insane this ability only needs 1 legendary/mythic item to spike and be abnoxious to enemies engages and damages paired up with her W this ability turns into a useful and unique utility

r - the ultimate is the most famous ability from orianna mid but in support your gonna use it but do no damage but still useful this ability because you're gonna use it for engage and disengage and dont have fear to use it just use it if you steal the kill who cares?

Champ select: Orianna is a acceptable pick as a Support but it depende alot on your teamcomp and enemy teamcomp.
You gonna pick Orianna when:
Your Teamcomp has a Aggressive ADC like Draven, Zeri, Samira, Lucian etc (it can work with Scale Champions like Veigar)
                        has a team that is good to put the Ball on like champions that need shield and more resistances to fight                                  melee or ranged
Enemy Teamcomp has Engage Support like Rell, Leona etc its acceptable against the same type champions as her
                           has good lane phase
                           has AP or Assassin Junglers like Karthus, Elise, Talon etc
                           has late game monsters on top lane like Tryndamere, Kayle, Tahm Kench and most tanks top

Runes:
for runes is simple
Aery and Resolve for Poke and Shield
Guardian and Inspiration for Burst Shielding and more tankiness (when the enemy use everything on 1 target and you need to block a great amount of damage quickly)

Quick Runes:

Aery -> Manaflow Band -> Transcendense -> Gathering Storm / Font of Life and Revitalize (minirunes you can choose whatever you like and is good in the game)
Guardian -> Font of Life -> Bone plate -> Revitalize / Magical Footwear and Biscuit

Advanced Runes: (if you want a detailed guide on the runes for a better optimization for the game in specific)

You're gonna choose Sorcery when enemies dont have a High Damage Early ADC and a Engage Support or a melee support in general (you can choose if you're against a shielding/healing champion and has a good amount of poke)
You're gonna choose Resolve when enemies have High Damage Early ADC and a Poke/Damage Support or a ranged support in general (your regular ADC Support and Mage Support like Zyra, Xerath and Brand)

Sorcery:

Aery - is the 100% recommended rune for Orianna because is good for Poke and Shielding in this path
Arcane Comet - if you choose violence today you can use Arcane Comet but is only good for Poke i dont recommend because the purpose of this guide is to play orianna utility support not orianna damage support but you can try with Imperial Mandate

Manaflow Band - this is the go to rune from the 3 orianna support as a Low CD shield that costs alot if spammed but if you're in a lane where you cant use alot of your spells your into specific matchups you can select one of the other 2.
Nullifying Orb - this gonna be just good against Full AP bot lane like Veigar ADC and Swain Support
Nimbus Cloak - this is not recommended but you can use if you're a KDA Selfish Player

Transcendence - this is and awesome rune for Orianna Support because her shield as low CD so with this rune mid game you're gonna be just spamming the shield with 3 seconds cd and can be a quickier cd if the enemy is killed and Ability Haste is good for any Mage
Celerity - this rune is good for Orianna, celerity makes you go quickier to lane and can help you roam if you think that the lane is lost based on the picks and your team is Early Winning the game and late game they are bad
Absolute Focus - in theory is a good rune for Orianna but in-game is just not practical most of the time you're gonna be low HP but if you dont need transcendence or Celerity you can use this rune

Scorch - is good rune for when you are against melee botlane
Waterwalking - is a good rune to pick with Celerity for the same reason and because they synergise 
Gathering Storm - is the best rune for Orianna support in this category because Orianna Support power comes mid-late game

Resolve:

Guardian - is the best rune in this path for orianna support because it shields a good amount of damage so its good into high damage enemy lanes

Demolish - you're never gonna use this
Font of Life - 99,9% of the games you're gonna use this rune because it was sinergy with your abilities (W and R)
Shield Bash - that is the 00,1% of the games you're gonna use if the shielding is not the focus the game but keeping you alive

Conditioning - this rune is awesome because it gives resistances for orianna after 12 minutes and orianna has base low resistances so this one is good for protecting yourself in teamfight because enemies will realise in the game that the Orianna Support is the problem and has to be eliminated
Second Wind - this runes is good for high poke enemy lane 
Bone Plate - this rune is good if one enemy has poke in lane which is 50% of the game

Overgrowth - this rune is good with Conditioning but never recommended because you really need one rune here in this category
Revitalize - this rune is the go to rune in this category
Unflinching - this rune is acceptable in high engage and slow poke lane

Secondary Runes:

Sorcery + Resolve - Font of Life - healing allies with slows and ccs
                              Conditioning - if you're gonna be the focus mid-late game
                              Bone Plate - if early game has poke
                              Second Wind if early game has tons of poke
                              Revitalize - you're gonna pick 100% of the times 

Resolve + Sorcery - Manaflow Band - if you need to trade alot
                              Transcendence - if you need to spam abilities mid game
                              Scorch - if enemy lane is 2 melees
                              Gathering Storm - mid-late game giga shields
                              Celerity - Roaming
                              Waterwalking - Roaming and Objective Fight
                              Nullifying Orb - if 2 mage lane
                              
Resolve + Inspiration - Magical Footwear - as a support you dont have alot of money so you need this for a free boot
                                  Future Market - if you want to have more itens and be in debt
                                  Cosmic Insight - good for utility
                                  Biscuit Delivery - good for lanes that you have to spam abilities

(or just use the recommended in LoLSolved)

In-game:

theres not much i can say to you because it depends alot on matchups, duos, kda's but i can advise you and say keep it simple dont think too much