This stuff will make your plants grow like crazy. You can sprinkle it around the top of the pot and water it in.
Mix it up with potting soil to boost growth of your plants or make "worm tea" by soaking the castings in pure water like a tea bag. An old panty hose or sock will work. This makes an excellent liquid fertilizer for all your needs. Steep overnight in a quart or gallon container, stir occasionally. Then continue to use until water is clear. Then the castings can still be used as a fertilizer as well.
You cannot harm plants by adding too much, unlike commercial fertilizer.
Castings are very light, a gallon bag will weigh about 5 lbs.