Hero Crates are the quickest way to unlock heroes. Each purchase provides one minimum three-star hero that is randomly selected from the Crate. You can view the list of available Heroes by tapping on the picture of the Crate. The ability to purchase 10 Crates at a time for a discount is available at higher VIP levels.
If you receive a duplicate of a Hero you already own, you will receive Hero Fragments that you can use to Evolve your Hero.
You can find the Hero Crate purchase option by tapping on the "shop" button at the bottom of your screen and then selecting the "crates" tab at the top middle of your screen. Please note that this list doesn't contain all possible awards, and may change from time to time.