BenitoRubenOrtizRojas I don't think any extension exists for this. You could use a combination of the pages extension or a discussion, and a link in the welcome banner or header links to point to that content.
You posted this in the dev tag, so are you looking to develop such an extension ? What part do you need help with ? The flagrow/direct-links extension might give you a good introduction to modals, and you can see how the flagrow/terms extension opens a modal on page load (though, not just after login).
