You might select this option if:
To use this option, simply make an account with Mendeley/Elsevier and begin populating references into your library through their website.
AND/OR
Download the reference manager for desktop, which works the same way as the web version, and also requires logging in.
However, if you want to work offline, you can select "make library available offline" after downloading, and it will sync and update your citations so you can work without internet. You will just want to sync next time you have internet access.
Recommended: Also install the two add-ons, the "Web Importer" and the "Citation Plugin." These will allow you to 'clip' citations from the web as you browse, and to add in-text citations and bibliographies to documents in Microsoft Word (from your Mendeley library) as you write.
You might select this software if:
Visit their website to download Mendeley Reference Manager for desktop. This is the legacy version of their software, the new one is "Reference Manager."
Recommended: Also install the two add-ons, the "Web Importer" and the "Citation Plugin." These will allow you to 'clip' citations from the web as you browse, and to add in-text citations and bibliographies to documents in Microsoft Word (from your Mendeley library) as you write.