I need an advice on how to play the last three campaigns

Guys, I recently bought Midnight but haven't played WoW since Battle for Azeroth, so I haven't played all the subsequent campaigns. My question is, I want to create a blood elf hunter and start from level 1. How can I level up while playing the campaigns before Midnight? (Shadowlands, Dragonflight and The War Within), do i need an specific level, where do i have to go to trigger the campaign?
thank you in advance!!