HTML5 is the latest version of the Hypertext Markup Language, the standard for structuring and presenting content on the web. Understanding the basics of HTML5 is essential for anyone looking to create or enhance a website. This comprehensive guide will help you get started by introducing key concepts such as elements, tags, and attributes. Additionally, HTML5 has introduced new features like semantic elements, multimedia support, and improved form controls, making it easier than ever to create rich and interactive websites.

To effectively utilize HTML5, it's important to grasp its structural components. Here are some fundamental elements you should know:

1. Doctype Declaration: Always start your HTML5 document with a declaration to inform the browser that you are using HTML5.
2. Semantic Elements: Tags like <header>, <footer>, and <article> provide meaning to your content, making it more understandable for both search engines and assistive technologies.
3. Forms and Input Types: HTML5 has enhanced forms with new input types like email, date, and range, improving user experience and data validation.

HTML5 is a significant evolution of the HTML standard, bringing with it a plethora of features that enhance the way developers create web applications. Here are the top 10 HTML5 features every developer should know:

1. Semantic Elements: HTML5 introduced new semantic elements that provide meaning and structure to your content. Tags like <header>, <footer>, <article>, and <section> not only make your markup clearer but also improve accessibility and SEO.
2. Audio and Video Support: Gone are the days of relying on third-party plugins for media playback. HTML5 provides native support for <audio> and <video> elements, ensuring that multimedia content can be easily integrated and played across all modern browsers.

Building responsive web applications with HTML5 is essential in today's digital landscape, where users access websites from various devices. To get started, you need to ensure your layout adapts seamlessly to different screen sizes. Utilize the viewport meta tag in your HTML head to control the layout on mobile browsers. This can be done by adding the following line: <meta name='viewport' content='width=device-width, initial-scale=1.0'>. Implementing a fluid grid system using CSS Flexbox or Grid layout can help structure your content effectively.

Furthermore, incorporating HTML5 features like the canvas element, audio, and video tags enhances interactivity and user engagement. Use media queries in your CSS to apply different styling based on the screen size or resolution. For example:

1. @media (max-width: 600px) {}
2. @media (min-width: 601px) and (max-width: 1200px) {}

With these techniques in place, your web application will not only be responsive but also provide a rich user experience across all devices.