SAP Business Technology Platform (SAP BTP) offers you the ability to turn data into business value, compose end-to-end business processes, and build and extend existing SAP solutions quickly.
Before starting with developing extension applications, you need to understand how SAP BTP is structured so you can choose the best components for your use case. Take a look at Cloud Foundry and Kyma environments, global accounts and subaccounts.
These are the best resources to start from: