In order to get an API key for importing YouTube videos in themes like goWatch you need to make sure you are logged in to your YouTube/Google accounts. Then, follow the steps from below:

1. Goto Google Developers Console and login with your YouTube/Google ID: https://console.developers.google.com/ 
2. Click the button Create Project, enter your project name in the New Project popup, Google will then create the project for you.
3. On the left menu, goto APIs & auth -> APIs, click YouTube Data API, in the following screen, click Enable API.
4. On the left menu, goto APIs & auth -> Credentials, click the button Create new Key

After clicking these you should receive a code which you can use for the importing process.