16.05. I have created an e-shop on the basis of the CMS. How can I install the payment platform?

You have to install one of the plugins suitable for your system. The plugins are provided at the address https://developers.paysera.com/en/payments/current#integration-via-plugins 

In case you cannot find the one you need, please refer to our specification when integrating: https://developers.paysera.com/en/payments/current#integration-via-specification.