While cURL has been around a while (20 years! cURL - Wikipedia), it's really new to many FileMaker developers. A brief explaination on the use of the supported options (FileMaker Pro 16 Help) and some real examples would help us get over the hurdle(s).
Show the differences (with examples) for: http, https, ftp, ftps, and file protocols as used by Insert From URL (FileMaker Pro 16 Help). The Data API is the next step (data to/from FMS), but this session should stick with Insert From URL (how FM can communicate with other APIs).
p.s. this may be similar (or an extension) to DevCon2017: INN004 - Explore cURL for FileMaker - Steve Winter