So this is really simple. Head over to the chrome appstore to download the extension. Now you can click the "Add to chrome" button in the top right to install the extension.
Now you'll get a cup of coffee and enjoy downloading any song by clicking the following button button:
When using the browser extension with SCD 2.7.0 or above, you have an option which will automatically quit SCD when the download completes. You can read more about this here...
You'll have to head over to the chrome://extensions/ (You will have to copy/paste that) page. Search for the "SCD" extension. Once found, click the trash icon to the right of it. Done!