Purpose

Before you start making your website, you need to think about two questions:

Why are you making it?

Being clear about the purpose of your website will help you to design it well. You need to think about what you want to communicate and explore how your site will do this.

Who is it for?

It's really important to identify your target audience (that is, people who will be coming to your site), and think about the site from their perspective. Talking to them will help you to understand what they want from your site.

Identifying the purpose of your site and exploring the needs of your target audience will help you decide how to structure your content and how to approach design.
Remember, you need to think like your audience, not like a website developer.