What is web browser ? What is a web server ? How are these two related ?

A Web Browser is a WWW client that navigates through the World Wide Web and displays web pages. For example, Internet Explorer, Google Chrome etc.

A Web Server is a WWW server that responds to the requests made by web browsers.

The World Wide Web (WWW) is based upon clients and servers. A web browser sends request to the web server and web server responds to the request made by web browser and fulfills the request accordingly. Hence, the web browser acts as a client of the web server.