1. Navigate to the API section
You will want to navigate to the API section here. You can do this yourself by clicking on Settings > API.
2. Click on Generate a new Key
Once you click on the green 'Generate a new Key' button, a pop-up will appear with your Client ID and Client Secret Key. Make sure that you save these somewhere as you will not be able to view them again.
That's all there is to it! You can view our documentation here which has information about both the merchant and store API's.