Designing a website is a process that requires a lot of thought and changes to get it just right. It requires feedback and modificatrion to meet your needs. A key way to visualize your website is with the use of wireframes and mock-ups.
Wireframes give you a bare bones look at the structure and layout of the website. It allows you to get a rough idea of how the user interface will look and where elements will be placed on your website.
Mock-ups are more detailed renderings of your website which resemble what the finished website would look like. Mock-ups add colour and more detail to allow you better visualize how the website would look when it is live.