This video shows some commands being used in a real world example. Please refer to Tutorial 2-3 for more information.
A lot of times you don't know the angle of a line, but you do know that it needs to be aligned to other lines. This is when you use these techniques.
The ALIGN command is NOT available to users of AutoCAD LT. For those people, the Rotate command will work just fine. It's good to know how to do things more than one way. You may end up working for a company that only uses the LT products.