If you use the same command often, you might get tired of typing it. bash lets you write shorter aliases for your commands.
Say you always use the --almost-all and --color=auto options to ls. You quickly get tired of typing ls --almost-all --color=auto. So you make an alias:
Now you can type myls instead of the full command. To see what myls really is, run the command type myls. To see a list of aliases you’ve defined, simply type alias on a line by itself.