Microdata are the syntax for embedding machine readable metadata in simple HTML. With this extra attribute added search engine is able to understand as close to human. To be exact, it adds great contribution for browser to understand what the piece of content is all about in a relevant way.
Let us take an example
Sudip Shrestha- 24, Male, Single, Engineer, Digital Marketer, Nepal.
Well, humans can contextually understand what the content is all about. But, for the computer program like a web browser or search engine bot, it is not as simple. To make computer programs understand what the content of the content is, the way as human do automatically do, we add microdata.