If you have the above macro defined in your source then you can have statements like the following:
align 32
This will advance the pc (program counter) to the next 32 byte boundary or leave it where it is if already aligned.
* is simply the current value of the program counter. &1 represents the first parameter passed to the macro, 32 in the example, so the macro call becomes the following code:
org * + (-* & 31)
All it is doing is adding just the right amount to the pc to achieve the required alignment. Note that the formula is really only useful for aligning to powers of 2.