The WordPress media library is the central location where all of the files you upload to WordPress are stored. The Media Library allows you to manage and modify those files. You can easily add descriptive titles and captions to your images, documents, and videos.
The WordPress Media Library also includes some handy image editing tools that allow you to quickly crop, resize, and modify photos.
This screencast also provides an overview of the WordPress media settings, explaining how each of the settings impact the way WordPress works with the media files that you’ve uploaded.