Ask HN: B2B software, state of the art?

I am trying to develop an app for my clients to use (small business) but inmediately got surrounded by terms like: microservices, SaaS PaaS, IaaS, etc... Now i dont know where to start, or what is the state of the art. Tried searching a course i remember from edx (SaaS on ruby on rails) but its archived. got the feel that this business model is a bit outdated or something new is trending. Is there any place to start?