Initially, you will see "frosting" on the area. (That's what you see in the videos online that make it look like the tattoo is being erased. See the video at the bottom of the page.) Within a few minutes the "frosting" will disappear and it will look like nothing was done to your tattoo. Your tattoo may even look darker.
You should notice some redness, swelling and/or bruising to the treatment site which is a normal reaction to the treatment.
Over the course of the next several weeks you will start to notice some areas of your tattoo starting to fade away. During the first few sessions this is most notable in tattoos with shading. Thick, dark tattoos are fading away but are working from the top down, so it may not look like much is happening with your first few treatments, but it is working!