When it comes to payment methodes it's important to know: The more, the better. This is why you should offer as many payment methods as you can to cover the most preferences possible.
It is that easy:
Hit "payment methods" and find the method you want to add
Fill up all the necessary fields
Choose the countries you want to authorize for this method in the drop down menu under "zone"
If not already done hit "zone configuration" to save more country groups
Just enter a price if you want your clients to pay an extra price for using this payment method (not recommended)
Save and you are finished :-)
Articles to the single payment methods are found here:
PayPal: http://helpcenter.branchbob.com/de/articles/2622388-offering-paypal-payment
Paypal Express: http://helpcenter.branchbob.com/de/articles/3807298-add-paypal-express
Credit card: http://helpcenter.branchbob.com/de/articles/2630724-offering-credit-card-payment
Bank transfer: http://helpcenter.branchbob.com/de/articles/2630847-offering-bank-transfer
Amazon Pay: http://helpcenter.branchbob.com/de/articles/2698860-offering-amazon-payment
Invoice: http://helpcenter.branchbob.com/de/articles/2630923-offering-payment-by-invoice
Cash on delivery: http://helpcenter.branchbob.com/de/articles/2630823-offering-payment-method-cash-on-delivery
Cash on pickup: http://helpcenter.branchbob.com/de/articles/2630881-offering-payment-method-cash-on-pickup