WordPress external API's

Hi guys I bought an external API's and I don't know how to integrate it into my WP site.
I start with some plugin but didn't works and I follow their tutorial but the API data doesn't appears on my website.
Do you know any plugin provide this option or an effective steps to do it?

I believe the following URL will be of use to you in your search.

https://stackoverflow.com/questions/28660995/best-wordpress-plugin-to-integrate-external-api´s