You can create a new entry by clicking on the third button (the one with a pencil on a sheet), or by selecting the “Add...” entry in the contextual menu on an item in the left pane.
The following dialog appears :
In the “ObjectClass” field, you must choose the object class of you new object.
In the “Relative DN” you enter the parent entry of your new object. This field has by default the value of the current selected entry.
In the “Fields” pane you can see the mandatory fields for the object class you selected. You can also choose the optional field that will automatically be added to you new object.
On you have entered all the values needed, use the contextual menu on the right pane to select the “Save” item.