In your dashboard, click “Developers”, then “API keys”.
On the “API keys” page, you can find both your publishable and secret keys under “Standard keys”. However, to reveal your secret key, click the “Reveal live key” button.
Test payments are called “Test mode” and real payments are called “Live mode” in your Stripe account. To switch between these two, click the “Viewing test data” toggle in the menu. Please note that each mode has different keys.