Hi, Misha,
First apiRequest, created in the file plain-function.ts is an abstraction of playwright requests, which takes a few mandatory parameters as request (playwright default fixture), Method and url, and a few optional - baseUrl,body and headers. After that we use it to create a custom fixure, where we attach automatiocaly the request, coming from Playwright, in order to have direct access to it through our tests.
Hope this is helpful to you. The best part is that the complete setup can be used in every Playwright Framework with minor reworks