Browsers like Internet Explorer and Firefox are designed to leave traces behind that indicate where you've been and what you've been looking at on the Internet. It's hard to absolutely guarantee that your activity on the Internet can't be traced at all.
To increase the level of protection it is recommended that you chose to browse the internet in "Private" mode when you don't want any history saved. By doing this your history is not saved, as well if you bookmark a page or download a document it is not saved in your browsers memory. When you close your browser window in private mode it returns to regular browsing mode.
Here are some simple things you can do to reduce the chances that someone looking through your computer will find out what you've been reading.