Adding a Graphic From Media Library
Adding a photo you have already uploaded to your blog
Ge the Image
Go to Posts -> Add New or Pages -> Add New, or open an existing post in editing mode.
Place your cursor where you would like the image to appear, and click on the (1) Add an Image icon found in the Upload/Insert icon group directly above your editor.
Click on the Media Library tab.
Select the image
Locate the image you wish to insert and click its Show link.
Edit Image information
You will be able to edit some of the image’s settings before inserting it into the post/page. Note that the fields will already be populated if you previously added the information when you uploaded your image to the media library. When done click on Insert into Post.
Text taken from Wordpress.com