Drop the bath bomb into the bath tub (to avoid a splash you can also lightly place it in)
Next you have a few options:
Option 1
Do nothing and let the bath bomb dissolve on its own
Option 2
Break it up into smaller pieces so it dissolves more quickly
Option 3
Hold it from below so it's half out of the water so you can control the fizz (and feel the fizzing action)
Lastly:
Once the bath bomb has dissolved, swirl the water around to evenly distribute the moisturizes that were in it.
Notes
It doesn't matter what the water temperature is, the bath bomb will activate once it hits any moisture (which is also why you want to make sure you store them in a dry place). As you can see from the photo below, it immediately starts to fizz when it touches water.