When you first sign up for a Stripe account it is set to test mode, where no real money is involved. Two sets of keys are provided, test and live. To operate the account in test mode, simply use the test keys. Copying the live keys into Payage will operate the account in live mode. Your Stripe account can be used simultaneously for both test and live payments. If you want to do that, you can create two accounts in Payage, one for testing, with the test keys, and another one for live, with the live keys. Make sure the test account is unpublished when your site goes live.