Fimming is actually no different that topping, what fimming does is virtually the exact same thing only your leaving part of the new growth. This only takes of part of the new growth and actually topping the very very new growth which is very hard to see.
What this ends up doing is making it seem as if your getting 4 new tops right next to eachother when its actually only 2 at the very top (like topping) but since it was cut so closely to the next newest set of fanleaves 2 branches which would have formed there anyways seems to make it look like there is 4 new tops.
This is how you go about doing this.
1. Locate the very top of the new growth
2. With a clean sterilized scissors, Fold the fan leafs over and cut approximately 80% of the new growth off the plant.
Thats IT!!!! you should be well on your way to Topping and Fimming of your plants.