I need to put the terms and conditions on the hotspot login page, but I need that the costumer mark the check box (I read the term and conditions bla bla..) before click enter. If they click enter before marking the check box, I need to show an error.
Google ‘javascript checkbox before submit’ and similar search strings. The idea is to not immediately submit the form, but to first check via Javascript whether the box is ticked and to either throw an error or submit the form for the user. Alternatively you could do things like show the submit button disabled and have an event trigger on the checkbox that enabled it when it is checked.
But really those are HTML questions and details about them should go into different communities.