You don't buy packs.

You buy monsters from the marketplace, which you can breed to make more and battle to level your player up.

Leveling up increases your ability of breeding rarer and stronger monsters.

When you reach the final level you also get the ability to get ERC20 in game powerups, called crystals, from battling.

Currently you can buy presale eggs which hatch into monsters upon mainnet. The eggs have gotten kind of expensive at this point since so many people have bought them: https://worldofether.com/eggs