I'm not sure that fimming is something you need to watch a video on. The link that bud88 posted is pretty good. Fimming is like a mini topping. Rather than cutting the main stem (and usually a growing tip or 4) as in topping, only about 1/2 of the new growing tip is pinched or cut off. I do this much more frequently than topping--I kind of hate to cut off great stuff that is growing well--and you usually get 4 tops as compared to 2 with topping. Some stains do not take to fimming or topping well. If you have a strain known for its huge central cola, I wouldn't fim or top. However, most strains take well to fimming
Indoor garden is defined volume illuminated w/defined light whose intensity is borderline useless only few feet away from source and nothing in known physics can change that for any light source for indoor gardening.
Therefore, every plant shoot should have a planed place in space in order to most uniformly fill the volume but guiding every sprig isn't doable in fact.
The best boilerplate to learn that direction is Top the young seedling, leaving only 4 good laterals about 90 degrees apart, close as possible in elevation.
3 wks max vegetative and full flower period will fill entire volume and if crop is over 42" tall at harvest, you're on backside of light/distance/yield curve.