I grew up with Pokemon TCG and MTG, but I've been weary of stepping foot in the digital TCG realm as I'm skeptical of how digital booster packs are assembled. Can anyone give me a rundown on how digital boosters are assembled?

Back in the day, if I saw a kid with a Charizard, he had to have gotten it from a booster (or card shop, whatever) but with online stuff, I feel like there's no guarantee that all cards are available. For some reason I just fear being shafted.

But I do really want to get into this game, so someone calm my anxieties please.