EndNote calls each collection of citations a Library. Each Library consists of 2 files, both of which are required. When you create an EndNote Library, a .ENL file with the same name as your Library, plus a .DATA folder are created. The .DATA folder is where all images, figures, etc. are stored. If you move your library to a different computer (or disc), or are going to share it, don't forget to move/share the .DATA folder as well.
There is a built-in tool in EndNote that will create for you a single file called a 'compressed library' that you can e-mail to others.
After you open a compressed library, be aware that EndNote has created a new library file and .DATA folder. Any changes you make will not be made in the .enlx file, but the newly created library file. It is highly recommended that you delete the .enlx file as soon as you open it with EndNote to avoid confusion.
If you want to send the library back, compress it with the steps above and send that new .enlx file.
EndNote stores all the changes you make as you are working. However, like any other important document, it is always a good idea to make a back up copy of your Library in case something happens to your computer or storage device.
When you back up your EndNote Library, make sure you also remember to also back up the corresponding DATA folder. You can back up your EndNote Library by using the 'Save a Copy' command from the 'File' menu to save a copy of your Library to the storage media of your choice (CD, USB drive, etc.).