A web developer is concerned with four aspects of a site.
Content is the raw material of a website. It consists of text, images, and other media such as video clips or sound files. Producing good web content is different from producing print content. A web page can be re sized, scrolled and can contain movies, sound files, links to other pages. and interactivity. People generally browse a web page, scanning a few key items then moving on, and they rarely read it word for word. In general have important content at the top of your page. Have clear headings and subsections, reinforce the text content with images.
Design elements include things like background images, color schemes, text fonts borders and decorations. They should compliment and not distract from the content of the page. It should direct attention to and reinforce the content. Ground up design can be complex, considering that it must work on a variety of devices (screen sizes and resolutions, mouse or touch) and deal with a huge number of parameters (text fonts and sizes for every style for instance and every possible screen resolution) For this reason nearly all design systems are based on a set of templates that deal to various degrees with some of these issues.
This is one of the things that distinguishes the web from print. A user interacts with a web site. They click on links, scroll, enter data and interact in many different and interesting ways. Architecture is how you organize the information on your site. Good architecture enables users to access the most important information with the least amount of clicks. How you name and structure menu items, what menus appear where on your site as well as how you categorize your sites content are key architectural decisions.
Increasingly web sites are becoming web applications. This includes things like user membership systems, shopping carts or member forums. They are usually implemented using modular add in components or plugins.