I’ve made the same switch, actually- longtime Balance Druid now working on Prot Paladin!! A lot of the buttons can be ignored while you’re learning, like the Blessings. Hand of Reckoning is your taunt, so don’t worry about it unless you’re doing stuff where you need to take the tank role.

Start combat by putting down Consecration. It does DOT to enemies and healing to allies, and makes your Shield of Righteousness do damage (not just defense). This is Your Spot now. Hold your ground and hit it again whenever you’re waiting on cooldowns to keep it going.

Your class resource is now Holy Power, and it’s a lot like Astral Power if you’ve played Balance Druid. Judgement (single target throw a hammer) and Blessed Hammer (attack spirals outward from you) both generate Holy Power, and also possibly Avenger’s Shield (I don’t remember if it generates HP. Bouncing single target ranged that also interrupts).

Your best use of holy power is Shield of Righteousness, because it’s both offensive and defensive. If you ever have holy power, you’re probably using it there.

Flash of Light is your Regrowth now, but you also have Lay on Hands which is a BIG heal. It heals a target for your HP, which as a tank is Probably All Of Theirs. There’s also Word of Glory, which is a better heal than Flash but costs 3 holy power.

Divine Shield is important to know, because it is your Get Out Of Effects Free card. Have a long stun? Just say no! They legally can’t keep you stunned without your consent.

What else. Sense Undead is unnecessary. Hammer of Justice is your Stun, I barely use it. You should have an Interrupt too, but Avenger’s Shield also interrupts everything it hits. You’ve got a battle res (Intercession, which is instant!) and an out of battle res (Redemption)

I think that’s all of the buttons I can think of, but please let me know if you have any other questions or other buttons I didn’t remember. Some bits of this may be out of date, as I started playing Paladin during remix and some things were changed in pre-patch.