Attribute mapping is done using either the attribute map panel in the AssemblyLine or in the component editor.
In the AssemblyLine editor you can add attributes either by right clicking in the attribute maps section and choosing add attribute, or use the Add button in the toolbar as shown below.
In this window you don't see the schema for the components in the AssemblyLine. To work with the schema you open the editor for the component by selecting it in the left tree.
The typical scenario for attribute mapping is to first discover the schema for the component. When you do a discover schema, the CE will run a background job that executes the query schema method of the component. If no schema is returned the CE will ask if you would like to read an entry to attempt to derive the schema from that. The result is then populated back into the schema for the component you are editing.
The picture below shows the contents of the input schema for a component after discovering attributes. If a component for some reason doesn't provide you with a schema you can add schema items manually using the Add… button on the toolbar or reuse a schema from another component configuration with the Change Inheritance option.
You can also use the drop down menu on the title bar to change the inheritance for the schema configuration.
If you have no schema or want to add attributes independent of the schema you can of course do so. Use the Add button to add a new attribute to the map. You name the attribute, and an expression of either "conn.attribute-name" or "work.attribute-name" is assigned to the new attribute. This can be done in both the AssemblyLine editor and in the Connector editor windows.
A dialog appears with an editable text field where you can type the name of the new attribute. The list above contains all known attribute names from the schema; you can select those you want added to the attribute map.
As you add more components to the AssemblyLine you can drag attributes between them where it makes sense. Dragging a component onto another component will map all mapped attributes to the target component. You can also drag attributes from the attribute map onto components in the left panel showing all components in the AssemblyLine. This will perform a simple map of all those items you drag over. This is similar to dropping them onto the component in the attribute map panel.
The concept of Attribute Mapping is treated fairly extensively, replete with examples, in IBM® Tivoli® Directory Integrator V7.1.1 Getting Started.
Depending on the Connector, and the mode it is configured in, there will be different tabs in the Connector configuration window.