Step by step
Login to your payever account.
Go to Apps > Checkout or directly open the Checkout application.
You will be able to see a preview of your checkout. You can setup the payment options you want to use under Payment options, activate the channels where you want to use your checkout and add more integration to your checkout via Connect.
Choose the order of the steps in your checkout under Sections and setup further settings under Settings.
You can find more information about checkout at this link: Checkout