The media library is the place where all of your uploaded media is stored in WordPress. Whether it’s images or videos or other types of documents, if you’ve uploaded it via WordPress, it’s going to be found in the media library.
To add images and other types of media from the media library into your post or pages, navigate to the Add Media button above the content editor’s toolbar. By default, the popup window prompts you to upload images or other types of media from your computer into WordPress.
To access things that you’ve already uploaded, on the left-hand side you’ll see Media Library. Clicking this gives you access to all the images and other types of media that you’ve uploaded already. Let’s select to insert this picture of a dolphin. When I click it, WordPress tells me that this is selected by placing a checkmark in the upper right-hand corner.
Over on the right-hand side we’ll see attachment details about the image, including its dimensions, title, caption and alternate text and any types of display settings that we’d like to play around with.
When everything is as you’d like it to be, in the bottom right-hand corner select Insert into Post. You can preview your changes before making it live on the web by selecting Preview Changes or click Update or Publish to publish your changes.