Open the EndNote library into which you wish to add a reference.
In the toolbar along the top, click on the New Reference button 
. Alternatively, click on the References menu and select New Reference. This will open the New Reference window. Select a Reference Type from the drop-down menu at the top of the window. Reference Type affects how bibliographic information is displayed in a citation.
Next, enter the bibliographic information for your reference in the Fields provided. Enter as much information as you have available. Do not include special formatting and punctuation when you enter bibliographic information into EndNote. The exception to this rule are the Author, Editor and Edition fields.
Author and Editor: Enter one name per line. Names can be entered either with the last name followed by a comma and the first name, or the first name followed by the last name. Enter full names whenever possible. If entering initials, place period or space between initials.
Edition: Enter as 1st, 2nd, 3rd, etc.
Once you have completed entering the bibliographic information, Save your new reference by selecting File > Save or, Ctrl + S on your keyboard. Your new reference will now be in your library and you can close the New Reference window.
New Reference Window
For further information: In your EndNote Library, click on the Help button 
in the toolbar along the top of the window. In the EndNote X6 Help box that appears, choose Entering and Editing References from the Contents. Then, click on Entering References. This provides information on entering information into specific fields.