There are many different methods for adding sources to EndNote. The most common are explained here and other methods are described under the extra details tab:
Importing citations from databases, SearchBox, or Google Scholar is the fastest and most complete way to add sources to EndNote.
From AU databases: Select citations you wish to import into EndNote. Locate the "Export" option in your database. It's usually located near the Save/Print/E-mail options. Select Direct Export in RIS Format. A Mac may require the additional step of importing from within EndNote.
From SearchBox: Save references to the folder by clicking the plus folder icon. Open the folder at the top of the page and select export to EndNote.
From Google Scholar (AU linked version): Change bibliographic manager under settings to show links to import citations into EndNote.
MANUALLY ADDING REFERENCES
Adding references by hand is the most time-consuming way to add citations to your library. However, it can be the best option when dealing with unusual reference types, complicated information, or for materials that cannot be automatically added. To add a new reference, click on this symbol from within EndNote: Be sure to select the appropriate type of reference before filling in the necessary information.