First of all, please make sure that you have Freemake Gold Pack key. Please remember that you can't activate Freemake Gold Pack with Subtitles Pack key.
1. Copy the key from the email.
2. Open Freemake Video Converter.
3. Go to Help-> Get Gold Pack-> Click “I already have a key”->Insert your key in a field. Make sure you copied only the key without additional spaces. Once you delete the space, the OK button should be enabled.->Click "OK". See the message that you've activated Gold Pack. That’s it. You can enjoy Gold Pack features now.