It is often confusing trying to understand what you can and can’t do with API’s and Webflow.
The Webflow API allows you to access data (fetch) and push new data to a site, from an external application / website. You don’t use it directly on a Webflow site, since there is no support for server-side programming languages on hosted Webflow sites. For that you need to build an app using the API and host it somewhere. Could you do that and then display stuff inside Webflow? Yes, if coded it.
Is it possible to combine data from multiple API’s or data sources? Yes, if you have a server running backend custom code, that gets and acts on data available via other API’s that you can talk to.