There are times when you need to route all your web traffic (http) and file transfer (ftp) traffic through a proxy. This may be because you're in a business environment and all traffic is "inspected" prior to going to the destination site or it may be at home where you've installed proxy software to monitor the kids or block them from some web sites / ftp sites.
Setting up the information in Linux to use the proxy is as simple as adding the following lines in one of several files.
This could be in ~/.bashrc (or other shell configuration file) or in /etc/profile. Both will accomplish the same thing. The advantage of using it in /etc/profile is that it applies to everyone using the computer. If it's in just your personal .bashrc file it only applies to your login.