So , since it's a HUGE game, I will cover basics of WOW as an ex newbie player.
Basically you need to do some Quests to level up to 80LVL to do some cool stuff.
Since this is 8x you will hop thru levels pretty quick , but here's a Map are by level guide :
Since this is 8X you will not need to do all the quests, leveling is quite quick and easy here , did mine char to 80lvl in 5 Hours or so. Addons like Quest Helper is a Must. Just download wotlk addons and drop them into your Wow/addons folder and then turn them on once youre in game thru Interface options.
Ridding Skill is important to level quicker , its costly - but its easy to get. Google Ridding Trainer and you will find everything you need to know about that.
Once youre 80Lvl theres Dungeons and Raids and Players vs Players Fun. For That you need gear , Emblems of Triumph and Frost are main currency to buy good iLvl gear. And theres a fucking difference in gear , like if you want to be good in Dungeons and RAIDS then don't ever wear gear that has RESILENCE - THAT GEAR IS FOR PVP(PlayerVsPlayer) only. If you do so , you might be called Noob or smth in that fasion by other players. Every Class have different Talents and Stat requirments and GEAR suited for that , so google youre Class Best Stats Cap.
When you get familiar with all that stuff then you wanna beat The LICH KING who is at Icecrown Citadel (ICC10-25 men). You want to be in Guild to do that, because you can ONLY enter 4 Times in ICC per week - 10 Men Raid/25 Men Raid/ 10 Men Heroic mode/25 Men Heroic Mode. There are 11 Bosses so make sure watch some videos on how to beat them before going there. All the best items will be here, once you beat Lich King you will get the Achievment and everybody will see that you are PRO. It's better to be PRO in here. Pro or Nob , thats how it works here. :D
Here's a video of boss: https://www.youtube.com/watch?v=Ocq4byvypZM
RESILENCE ITEMS - are ment for Players vs Players, battleground stuff and ARENA 2-2/3-3/5-5 team championship :D You will collect Honors Points and Arena Points for those items, vendors for those items are mixed, you will find them all in Dalaran. PVP is really fun , just like Fortnite, but for smarter people... :D
This is one good example of how to 2 vs 2 teams are beating each other up : https://www.youtube.com/watch?v=Z4095YVCD7Y
Hobbies like Achievments / Reputation Gaining / Proffesion / Rare Mount hunting is very wide and cool too.