Hello Federica =)
The answer to this question depends a bit on what you're looking for!
If you're a beginner to programming, and you want to use blocks to code something, then using Blockly directly is not your best bet =( Blockly is a library that other applications use in their web pages. So you want to use one of those applications instead! E.g. Scratch, Code.org, MakeCode, AppInventor, etc.
If you are a developer, and you want to integrate Blockly into your web page, then I recommend starting with the
getting started codelab. If you still run into issues, feel free to post them back here!
Best wishes,
--Beka