Different ways to interact with SAP system from a web application

Using any of above method depends on what you are connecting, and version of your SAP system. You can use Standard BAPI’s to read or update a service order. BAPI is a Remote Function Call RFC with a standard API.

In latest releases of SAP ERP, many of Function Modules are exposed as Web Services.

In SAP system, you need to follow some administration task to allow access to SAP system. Following T-Codes can be used: SICF or SOAMANAGER.

When you install ABAP Application Server, all the services are available in an inactive state. When a call is made to a URL, multiple services are executed and all service node must be executed in SICF tree.

To activate a service, select the required ICF service in the ICF tree in transaction SICF.

Activate the ICF service in one of the following ways:

• You have to use Menu option Service/Host →Activate
• You can also use the context menu and be choosing Activate Service.

In some of the scenarios, if you are using SAP PI/XI or any other non-SAP Integration Engine, it would be easier to connect but with limited functionality.
https://www.tutorialspoint.com/sap_pi/