In order to get a YouTube API Key you will need to create a new project on the Google Cloud Platform, click the hyperlink and insert as name "Latest Video Popup", this will help you recognize the project in the future; the click on Create.
Wait a few moments until the project get created and then select it from the dropdown menu on the top left of the screen, the one next to the Google Cloud Platform logo.
Now we need to enable the YouTube APIs for this project, to do so just type into the search bar on the top of the screen "YouTube" and then select the option saying "YouTube Data API v3", let the page load and click on the Enable button.
Now that we have a project and we have enabled the YouTube API we can finally get the key we're looking for, to do so select the Credentials option from the left side menu and then click on + CREATE CREDENTIALS > API KEY and here you have your API key.