On the left toolbar, click on Sales and then Settings.
Click on Payments tab.
Find Stripe from the list of payment methods and click Setup on the right.
Tick Enable.
To test if payments work, you must enable Test Mode first and enter the Test Publishable Key and Test Secret Key obtained from your Stripe account. Here’s a documentation on where the keys can be found.
Once you’ve tested that payments are coming through properly, you can now disable Test Mode by unchecking Enable Test Mode. The key fields will be replaced with Live key fields so you need to make sure you replace the TEST keys with the LIVE ones.
Don’t forget to click Save Changes every time you edit the settings.