You have two API keys, a secret API key and a publishable API key, associated with your Stripe account - they are used mainly for identification on the server side and the application side. The publishable key is used to generate credit card tokens and should be used with Stripe JS library. The secret key is used for all other API calls on the server-side. For more info, here’s the stripe.js documentation on Stripe and the stripe.js documentation on Chargebee.
If you want to work stripe.js into your in-house checkout page then you should keep your publishable API key at the ready, as it is what sits at the heart of communicating via tokens. You can find it at Account Settings >> API keys on your Stripe web interface.