How to buy heroes in Heroes of the Storm?

Excuse me, I'm trying to figure out how to purchase heroes in the game Heroes of the Storm. Could you please explain the process in a straightforward manner? Are there any prerequisites or steps I need to follow before I can make a purchase? Also, are there different ways to acquire heroes, or is buying them with in-game currency the only option? I'm quite new to the game and would appreciate any guidance you can provide. Thank you in advance!