Web sites have three primary components: design/layout, content, and logic. Design is the visual appearance - what it looks like, how the screen is organized. Content is the information conveyed - and it may be text, audio, video or a combination thereof. Logic is the engineering that makes it work - it can be a commercial open-source application, or it can be custom code, or a mixture.
Design usually begins with wireframes, simple text representations of what will be on the page and where it will be. The text may describe images as well. Once that is established, comps (image of the screen) can be made. Often, a comp is made for the home page, and another is made for internal pages.
Content is an extremely important part of the site. There are two types of content - structured and unstructured. Structured content contains common data elements - like an address book. For an address book, each address would be considered structured content, and the site should manage the data in as such. Unstructured content is blocks of text or images that do not share common data elements - the blog posts in this blog are a good example of unstructured content. Discriminating between the two content types should be done by the person responsible for the logic (usually an engineer).
Logic is what brings the functionality to life. If you are trying to sell something, logic will be a cart - and you should definitely use a commercial cart instead of trying to build one. If you are trying to inform your visitors, you should consider a content management system, or a blog. Again - don’t reinvent the wheel, buy or use an existing system. Custom code has its place, but it is very expensive and risky.
Design and content definition should happen before logic. In a nutshell, what will it look like and what does it have to do. Content definition often dictates the logic. Engineering should be part of these stages, but, the engineering tasks can and should be defered until the bulk of the design and content have been defined. If there are clear, established, requirements for functionality, engineering can be done concurrently, with integration performed later.
The most important part of the process is to focus on the objective of the site. What is this site supposed to do? Who are the target visitors?