When using ChatGPT to generate data for the first time, a pop-up window will appear asking you to set some options, including whether to use your own API Key or use the service we provide for you.
If you choose to use your own API Key, you need to go to Open AI and generate your API Key (go here). If you choose to use the service we provide for you, we will default give you 10,000 tokens as a gift. You can see your balance in the settings page.