Semantic search, what does it mean?
Let me show you a common situation.
The word "Avatar" can have more meanings: it could be a film title, an user image on a forum and a lot of other things. We can understund what we're talking about using the context, a machine can't, it needs more information.
For this reason schema.org dictionary was created: adding its elements we can define if a man is a director movie, the length of a video or how many comments an item received.
WHICH ARE THE EFFECTS?
So, by now, a question should popped inside your mind: "Very nice, but why should I take this extra work?".
Adding these tags won't make you climb position, but you'll have much more: your results will become nicer than simple links since they will be transformed in "rich snippets".
Joomla4Schema.org is a visual editor for schema.org attributes: you can add them quickly to your pages, you only have to select the text you want to "enrich" and you can start adding attributes.
Here you can find a video that shows how you can use this tool: