This documentation is from official magento 2 website.
https://devdocs.magento.com/guides/v2.4/payments-integrations/payment-gateway/payment-gateway-intro.html
This video tells step by step after you login into admin side -
https://www.youtube.com/watch?v=nl_lMB4fqwk
Detailed Video
https://www.youtube.com/watch?v=eoUBLxKa0pQ
Thanks
Vibhore

This documentation is from official magento 2 website.
https://devdocs.magento.com/guides/v2.4/payments-integrations/payment-gateway/payment-gateway-intro.html

This video tells step by step after you login into admin side -
https://www.youtube.com/watch?v=nl_lMB4fqwk

Detailed Video
https://www.youtube.com/watch?v=eoUBLxKa0pQ