Cookies and internet cache is the way the internet get's on your computer, as cached; temporary, or "live" So that you can see whats on a website; as well as login information for places like this, so that you can post or see "new posts"; they see you have a cookie from them already and say; ok don't need to download such and such images; look on c:\internet_cache\day one two three etc... "hypothetically"... so it's important to clear your temp cache, cookies etc, that way you don't have "out dated" cached files taking front stage to the up to date content you are trying to access...

Speed of surfing is mainly dependant on your service provider and other things like traffic load at a particular time of day etc....