Warning: All activities on a computer can be monitored
There are many ways activities on a computer can be monitored, including:
Keystroke logging programs
It is possible for a person to install a small program called a keystroke logger that runs 'in the background' silently making a record of all keystrokes typed into that computer. Later, the person who installed the program can access the keystroke log and learn exactly what other people have been doing on the computer.
Web browser history
Your web browser normally keeps a record of every website you visit in a 'history file'. This file is usually cleared out automatically after a period of time, but that time is typically a week or longer, so it is possible for someone to review the browser's history to see where others using the computer have been online.
Web browser cache and cookies
Many people know about the web browser history file and use their browser settings to 'clear history' thinking this will remove traces of where they've been online. But the web browser also stores other things which can be used to identify where a person has been online. Every time you visit a webpage, your web browser saves a copy of things like images on the webpage in a hidden area on your computer called the 'cache'.
It does this because usually when you are viewing a website and you browse from page to page, many of the images are the same, so the web browser just uses the images it saved in the 'cache' instead of having to retrieve them again from the remote website. This makes web browsing faster and more convenient. Unfortunately, it also means that after you leave the computer, these files are still around and someone may look in the cache for clues as to where you have been browsing.
Many websites also use 'cookies' which are small text files stored on your computer and hold data specific to one website. A typical use for cookies would be to save your username so the next time you login, they can greet you with a 'Welcome back Mrs. Smith' personalized greeting. Many normal online activities, such as online purchasing, rely on cookies to work properly.
Unfortunately, it is very easy for someone to view these cookie data files, and determine which websites they are associated with. Your web browser allows you some ability to clear out these cache and cookie files in the browser options, but there are places where cookies can be placed which are not affected by the 'Delete Cookies' or 'Delete Files' features of web browsers.
Be safe!
If you need to make sure someone does not find out that you're using this website, do not access this site from your home computer.
Instead, access this site from a public computer at a library or similar situation and not from a computer the person you're concerned about would know you've used.