Here you can set your logo and favicon. You can upload logo/favicon image or you can paste link to it directly into the field.
To upload or select previousely uploaded image - you need to click "Upload" button.
Then drop/select files to upload image or switch tab to "Media Library" to select previousely uploaded image.
And click "Use this Image" inside tab of the image data (you need to click "show" if you open "Media Library" tab).