First time playing WOW leveling priest.Need help with build!

So i started to play on this server about 3 days ago.Im level 20 atm but now i want to play harder to get to max level asap.So i need help with leveling build to get there as soon as possible.If someone please can help with some pointer,just to know what talents to pick and what spells are best to use.
Oh and yes i have huge problem with mana atm so i was wondering do i do something wrong or its just current situation?
I plan to go full heals once i hit max level but for now i need good trash cleaning build.
I should also state that this is my first time im playing WOW.

You picked the absolute worst class when it comes to leveling, my advice would be to make something else that has easier time with leveling - hunter is great for beginners. If you're set on playing priest then level as shadow. First thing yo need to take is spirit tap, it'll let you regen some mana after killing enemy, after that you can follow this build https://wotlk.evowow.com/?talent#bZZhxfdofkffofkAo, once you get those 51 points in shadow at lvl 60 you can spend the rest however you like, taking talents you deem useful from shadow or going into discipline to get some more dmg and mana regen.

Make sure you stack up on mana drinks as you'll need to sit down and regen your mana every few mobs you kill, early on as often as every second one. Dont use shadow word pain on every enemy you take as its very mana inefficient, holy fire is your best friend there.

Prioritize intellect on the items that you find, after that spell power and spirit are also good, stamina will help you not die but usually you'll only die if you go out of mana due to ability to heal yourself.
Its also possible to level with healing spec by using random dugeon finder but you'll alos have cripling mana issues there.