By default, the Author theme will create a basic text logo from your ‘Site Title’ (Settings -> General).
If you have an image logo to upload, you can do that using the built-in uploader.
- Navigate to Appearance -> Customize.
- Press ‘Author Theme’.
- Press ‘Header’.
- Press ‘Select Logo’, then use the uploader to upload and select your image.
- Press ‘Save Changes’.