I have a html page and a drop down menu on top. The drop down menu is for like users. The user has to pick their role and based on that, the page will only show some parts of the content.
So I have the drop down on top and based on what they pick, hide the contents that they're not supposed to see.
Is this possible with HTML? What do I need to do?

It is not possible to hide document content or HTML encoding from a user in the basic case. If the data stream is downloadable by the browser to be rendered, then it is available to the user to see as well.