RESTful webservice or REST API is basically the most common form of microservices.

Learn all you need to know about API’s (building and consuming) on Learn to code and help nonprofits for free and go specifically to the API Projects section.

In order to understand REST API’s you need to learn about JSON and how to handle JSON which can be learned there as well.

Most REST API’s will only work if you have some sort of authorization. All data which is not for everybody to see is behind some identifying system. The most used form of authentication and authorization is through OAUTH (2). So usually you provide credentials (which you have created yourself) to retrieve a token and which every call to the REST API Microservice you put the token in the header.

This answer is IMO a great start to explore and understand microservices. They are a bit hard to get if you are new to programming, but once you get beyond that, it’s pretty easy and straight forward.

If you just want shallow knowledge? Open a Google Cloud Platform account or an AWS account and first use the console to do stuff like uploading a file with S3 and access it through HTTPS, then find your Access Key and Secret Access Key (your token pair) and try to upload or retrieve a file through AWS API which is of course a microservice.

For more details or tutorials visit here.