HTML5 is important because now that all major vendors support it – including those in the mobile space – you get a universal experience across a wide spectrum of devices.Accordingly, with HTML5, you get device ubiquity. You get a chance to build something once and have it work across a wide spectrum of browsers.
CSS handles the look and feel part of a web page. Using CSS, you can control the color of the text, the style of fonts, the spacing between paragraphs, how columns are sized and laid out, etc.
JQuery is your best choice if your project primarily involves a level of DOM manipulation, easier approach to Ajax, animation effects, hooks or events. JQuery provides a user friendly environment to complete the things with ease. It plays a vital role for Web Developers.