Adding an alias to your system is a good way of saving time when remembering complex commands. You can reduce a command down to a quick two letter command that is easy to remember.
The alias command can be used to assign an alias on the fly. You can create an alias to 'ls -lah' by typing in the following into the command line.
alias ll="ls -lah"
Now, when you type 'll' (i.e. two lower case L's) you will actually run the command 'ls -la'.
Or you might want to do more complex things like running your selenium server.
alias selenium-server="java -jar ~/Development/selenium-server-standalone-2.25.0.jar"
To remove an alias you can use the unalias command to remove an alias from your system.