1. Extract the chrome.zip you downloaded to your Desktop.
2. Open Chrome->Settings and Select "Extensions" on the left navigation bar.
3. Tick the "Developer Mode" checkbox.
4. Select "Load unpacked extensions" and select the folder that you created on your desktop during the first step.
5. And you're done! Now you can just click "Get Mp3" or "Get Video" while browsing YouTube to download the video :)