Clearing cache and cookies insures that you see the most recent version of your website.
Modern web browsers often download web pages and store them on your computer in your cache or with the help of cookies. When you visit a web page again, the browser speeds up loading time by displaying the downloaded version from your computer, instead of downloading the entire page from the web again. This is great for speed and data, but sometimes, you'll see an old version of a website.
Clearing your cache and cookies will prevent this.
How to clear your cache
Note: These things change! For the latest instructions on clearing your cache, just Google how to clear cache for your browser.