What is the difference between azure API-apps,logic-apps,web-apps and azure functions? And what difference does it make for developer?
Logic Apps:
Logic Apps provide a way to simplify and implement scalable integrations and workflows in the cloud. It provides a visual designer to model and automate your process as a series of steps known as a workflow. There are many connectors across the cloud and on-premises to quickly integrate across services and protocols. A logic app begins with a trigger (like 'When an account is added to Dynamics CRM') and after firing can begin many combinations actions, conversions, and condition logic.
Api Apps:
API apps in Azure App Service offer features that make it easier to develop, host, and consume APIs in the cloud and on-premises. With API apps you get enterprise grade security, simple access control, hybrid connectivity, automatic SDK generation, and seamless integration with Logic Apps.
Web Apps:
App Service Web Apps is a fully managed compute platform that is optimized for hosting websites and web applications. This platform-as-a-service (PaaS) offering of Microsoft Azure lets you focus on your business logic while Azure takes care of the infrastructure to run and scale your apps.
Functions:
Azure Functions is a solution for easily running small pieces of code, or "functions," in the cloud. You can write just the code you need for the problem at hand, without worrying about a whole application or the infrastructure to run it. Functions can make development even more productive, and you can use your development language of choice, such as C#, F#, Node.js, Python or PHP. Pay only for the time your code runs and trust Azure to scale as needed. Azure Functions lets you develop serverless applications on Microsoft Azure.
Api apps and Web apps are pretty much the same deal. Logic Apps and Functions are the same in a sense that they allow you to do something as a response to event or on a schedule, but Functions are a way to run code (or existing app) and Logic Apps are more like a workflow constructor, where you take existing actions and chain them (so no coding, or almost no)
ps. You can easily find documentation for those online to get a broader understanding