1) Not sure exactly what you are referring to here. Suggest you check the WSAD Help.
2) The wizards in WSAD make it simple. All that is required is:
a) Create an EJB using the EJB wizard.
b) Create one or more methods and promote to the remote interface.
(from the Outline view)
c) Build the EJB project.
d) Generate deployment code. (from the EJB project context menu)
e) Add the EJB jar in to the EAR deployment descriptor.
f) Start your
test server and use 'em.
3) ejb-jar.xml is the standard EJB deployment descriptor.
ejb-jar-ext.xmi is the descriptor containing IBM, i.e. non-J2EE
extensions.
ejb-jar-bnd.xmi is the descriptor containing bindings like JNDI names,
i.e. more non-J2EE stuff.
You should be able to find more detailed information in the WSAD Help.