stop surfing , doing porn, and internet things in general
some cookies come from the likes of the bbc, nhs, answerbank, your bank .... etc etc ....
some remember IDs, passwords, preferences, address, location .... some just remember what you were looking at last ... they are not all bad.
you can delete them all .... but you can't be selective without going through them one by one.
and obviously the ones from your bank don't identify themselves so blatantly
this makes life a little easier
http://www.ccleaner.com/download