The Diablo Immortal Shop is an in-app purchase section within the game where you can purchase materials, crests, bundles, services, and currency.
You can access the shop by clicking the 3-line icon at the top-right corner, next to the mini-map. This UI will open. Here you can click the SHOP button. This article will show screenshots of the features within the shop.
Here is a preview at some of the features that may be purchased with real-money via the Google Play payment system. You can purchase with a credit card or PayPal.