Example
One way to create a macro is to record it.
Start recording a macro and save it to a register (in this example, we'll use a, but it can be any register you could normally yank text to):
qa
Then run the commands you want to record in the macro (here, we'll surround the contents of a line with <li> tags):
I<li><ESC>A</li>
When we're finished with the commands we want to record in the macro, stop the recording:
q
Now, any time we want to execute the recorded sequence of commands stored in a, use:
@a
and vim will repeat the recorded sequence.
Next time you would like to repeat the last macro that was used you can double type @:
@@
And as a extra bonus it is good to remember that if you put a number before a command it will repeat it that many times. So, you repeat the macro saved in register a 20 times with:
20@a
