Its a long process that requires ice, buckets, bags and something to stir with. I learned the technique from watching BubbleMan on youtube. Essentially, you add your materials and ice into the bag within other bags. You'll add water and stir, which breaks the trichome heads off and into the water. You then let the bags out of the bucket and let the water drain into the other bags. Depending upon bag micron (screen) size, you will have different grades of trichome heads.
This is a great way to turn your trash into stash. All of my trim that would normally get tossed out, is saved and then used in the bubble bags once I've collected enough material.