The word plan is quite broad and is used here for that very reason. When developing a site (using any technology) you need to plan
- your project resources, schedule, and budget (to name a few project management planning tasks)
- how your site will be organized
- how your content will be stored, organized, and reused
- how your users will interact
- how your site will look
- how the process tasks that will be required or needed to sustain your site
- what features or functionality you will want
- and so on.
Planning is a success factor that I strongly recommend you don't take lightly.