Why SAP? SAP is the most dominating company in the Business Application World. Yes, SAP is for big enterprises [SAP recently released software for small and mid-size companies]. The earnings of the SAP professionals are also very high. Microsoft is dominant mostly in the personal computer software/os domains. However, SAP, IBM, Oracle, and Sun are the most dominant companies in the business application world.
Though computer science is not about business/application software but about system software, still most computer students are employed in the business/application software area. Yes, IT and CIS are about business/application software.
SAP has different modules like CRM, SRM, SCM, and many others. Search this web-site for more articles on the overview of SAP. It's better to find an area of interest in SAP and be expert in that. Afterwards, you can try to learn other modules as required. In mySAP ERP, ecommerce/webshop is a recent extension. It implements enterprise ecommerce systems on top of SAP.
SAP Ecommerce Framework has three layers: Interaction and presentation layer, Business object layer (BO Layer), and Business Logic Service Layer (BLS Layer)
Presentation Layer: SAP favors JSP in terms of presentation layer. SAP extensions to JSP include: Custom ISA tags, MimeURL, WebappsURL, translate, iterate, contentType, message, imageAttribute, moduleName.
In presentation layer, you also need to be familiar with dynamic field control concepts such as UI element objects, UI element group objects, and configuration of fields via XCM admin, xcmadmin-config.xml file, and conf-data.xml file.
Interaction Layer:You should be familiar with the UI components, Interaction Components such as Actions, Threads in Actions, ActionForms, Interaction configuration like ActionServlet, ActionFormBean, ActionMapping, ActionForward, ISA extensions of struts such as com.sap.isa.core.InitAction, com.sap.isa.core.BaseAction, com.sap.isa.isacore.action.ECOmBaseAction, com.sap.isa.core.UserSessionData, and also multiple languages integration using resource keys.
Interaction layer includes some other additional concepts such as Input Validation, HTTP Header Information, Cross Site Scripting, User Authentication. You are also required to master these concepts.
Business Object layer includes different business objects such as Customer, Order, and Basket.
Business Logic Service Layer (BLS Layer): You need to master the Backend Objects, Backend Object Manager, Connection Management such as JCo based connections, and Working with JCo functions.
BLS also includes a Message Framework that includes messaging classes such as Message, MessageList, and MessageListHolder, Message Tags, and default error pages such as appbase/backenderror.jsp.
BLS also includes a Generic Search Framework, also Logging and Tracing capabilities.
Reference: SAP Developer Extension Guide - SAP Ecommerce 5.0