A full documentation link can be found here: https://shopify.dev/docs/apps/getting-started

What’s the purpose of a Shopify app?

• Extends functionality of Shopify
• Add more features or improve some existing features (e.g. Custom checkout flow)
• Integrate with external services (e.g. delivery services like UPS)
• Pull and use Shopify data in your app, platform, integration

How apps fit into Shopify?

• Use Shopify APIs to read and write user’s store data in response to different events (webhook events)
• Extending new features inside existing parts of the Shopify admin
• Enhance the way stores display info to customers

How to start building an app?

• Before starting make sure you have a shopify partner account
• Use ShopifyCLI to take advantage of the app template
• Or can always start from scratch (using APIs and follow authentication flow, then call their APIs to read and write data)

Authorization and authentication

• Must complete authorization and authentication before working with merchant and Shopify data
• Authorization means the store merchant gives the app permission to access data in the store e.g. orders, products, etc.
• authentication means Shopify verify the identity of the user of the app; all apps connecting to APIs must authenticate before making a request
• authentication simplified by using a access and refresh token

Types of authorization and authentication methods

• Depending on how you create your app and the components your app uses, you will be prompted to use different authorization and authentication methods
• Apps created with Shopify CLI or through the partner Dashboard use OAuth
• Apps embedded in Shopify admin using App Bridge use sessions tokens
• Apps created in Shopify admin use access tokens generated in the Shopify Admin

Summary:

This note captures at a high level what the things you need to follow and use when starting to work on a Shopify app. In my experience, when creating a Shopify app, many people use Shopify CLI with Shopify supported libraries (Ruby, Python, Js, etc.).

Last but not least, having a solid understanding about OAuth is quite beneficial especially if you are not using Shopify app templates.