A web browser, also known as an internet browser, is software that is used to display information from the internet.   Although web browsers are primarily intended to access the internet, they can also be used to access information provided by web servers in private networks or files in file systems. Some browsers can also be used to save information resources to file systems.  A file system being a method of storing and organizing computer files.  These files get organized and put into a database for the storage, manipulation and retrieval by the operating system.
One of the most common web browsers is called Windows Internet Explorer (IE).  This is a series of graphical web browsers developed by Microsoft which is included as part of the Microsoft Windows line of operating systems. IE has been the most commonly used since 1999, arriving at a peak market share of about 95% in 2002 and 2003.  Since then, its popularity has decreased due to competition from other web browsers to 55%, and is slowly trending downward.
One of the web browsers responsible for the decline in IE is called Mozilla Firefox.  It’s a free open source web browser.  This is the second most popular web browser as of September 2010 with approximately 23% of the market.  Mozilla Firefox's market has grown each year since the beginning.  Downloads of Firefox have continued to increase since Firefox 1.0 was released in November 2004.  As of July 31, 2009 Firefox has been downloaded over one billion times. This number does not include downloads using software updates or those from third-party websites.  It also does not count individual users, as one download can be installed on many computers.  
Another competitor in the web browser market is Opera.  Opera is known for initiating many features later adopted by other Web browsers. Regardless of this, Opera has captured only a small fraction of the web browser market. Notwithstanding, it does, though, have a stronger market share on mobile devices such as mobile phones, smartphones, and personal digital assistants.
Safari web browser developed by Apple.  First released in early 2003 as a public beta.  It soon became Apple’s default browser.  It is now available as a free download for both Mac and Microsoft Windows.  Safari is the fourth largest web browser as of 2010 behind Google’s Chrome whose reception was not great in the beginning but after a slight decline began seeing an increase in usage.
There are many other web browsers from which to choose.  It really depends on what you prefer.   There are similar features among the competitors and well as features that distinguish them apart from the others.  Determining what your needs and wants are will be the way to choose the one that suits you.  You can also download these different web browsers assuming your computer meets the minimum requirements.  Take a test drive with some of the web browsers that interest you and make your decision by using each one for a period of time and making an evaluation.