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.