From end-user point of view, he doesn't know how the backend of the application runs. It might be just a single server hosting the entire website in the very early stage, or a dozen of servers in a data center, or more luckily, if the company survives long enough, several large cluster running in different regions.
The application evolves all the time when delivering business capabilities. During the transition, we might see the backend evolving from a monolithic application to a collection of decoupled services, with mature pipelines, infrastructure, etc.
Microservices architecture is an architectural style that structured applications as a set of loosely decoupled services. The advantage of microservices architecture is it enables large and complex application to continuously scale and evolve.
The microservices architecture is a well-proved architecture style by many companies. It's very likely a single application might eventually evolve to considering we're in cloud-era.