New to white mage and need help.

[Risvertasashi]

The difficulty of healing, especially while leveling, is almost entirely about how good your tank's gear is. If you're in a leveling dungeon spamming cures and you still can't keep up either your tank has really bad gear, is pulling too many mobs at once, or both. Tell the tank to slow down.

Not entirely.

It also does depend on the healer's gear. So Bearyboring, my first suggestion is to make sure your gear is up to date. Especially weapon and left side gear. But try not to neglect anything. If you haven't been lucky with drops, there are vendors that sell basic gear and some nice players may even be willing to make you some for free.

Now, tank gear. That is important, yes. Before level 50, tanks can wear DPS gear too, which makes them super, super squishy. So, examine your tank at the dungeon's start. If they're wearing DPS gear, ask them nicely to switch to wearing tank gear. If they're simply undergeared... not much you can do there except ask for small pulls.

Finally, your spells. At a minimum, go to your role shared actions screen and make sure you have "Largesse" and "Lucid Dreaming" equipped. First you want to use "Regen" on the tank (if you haven't unlocked Regen, you need to catch up on your class quests). After that... assuming you have a glass tank... spam cure for more efficient healing and cure 2 for more powerful but more expensive healing. Do not use cure 3 as a tank heal ever.

Largesse will add an extra bit of oomph to your healing. If you know your tank is fragile, use it before regen, otherwise you can choose to use it reactively. Lucid Dreaming, just make sure to not wait until you're out of MP to use it. Around 70% MP is OK, particularly when you know you have a lot of curing ahead.

Good luck.

[Zeromon]

... my first suggestion is to make sure your gear is up to date. Especially weapon and left side gear.

I agree with this. I'm not sure if the following is proven out but I recommend being within 10 levels between each piece of your gear and the dungeon level (this is especially important for your weapon and left side gear). Any more than that and healing becomes extremely difficult (until level 50 where item levels are desynced from character levels). Risvertasashi's adice for healing is spot on. If you need to spam heals don't be afraid to. Also take advantage of Presence of Mind for healing, and use Lucid Dreaming generously. Take advantage of freecure procs and any other long cooldown ability. If you need a cure 2 immediately don't be afraid to burn a swiftcast even.