Please go to the BEA's website for complete documentation of weblogic servers. You need to understand the basic concepts of web applications. BEA provided a very good online documentation.
Pl visit e-docs for weblogic platform 7.0
Here is the definition of a web application as defined by Bea
"A Web Application contains an application's resources, such as servlets, JavaServer Pages (JSP), JSP tag libraries, and static resources such as HTML pages and image files. A Web Application can also define links to resources outside of the application such as Enterprise JavaBeans (EJBs). Web Applications deployed on WebLogic Server use a standard J2EE deployment descriptor in conjunction with an optional WebLogic-specific deployment descriptor to define the resources and their operating parameters.
JSP pages and HTTP servlets can access all services and APIs available in WebLogic Server. These services include EJBs, database connections through Java Database Connectivity (JDBC), JavaMessaging Service (JMS), XML, and more. "