The Media Library is where your images and videos are stored. Once an image or video has been uploaded, you can always use it on as many pages and posts as you’d like,
You can also store and use other docs that you can link to for your site. Example? If you like to have users open or download a pdf file you can upload and store it in the Media Library.
Note: It’s a bad idea to upload very heavy files to be used for your site. File sizes that exceed 100KB are not a good idea especially for those using slow WIFI networks.