I bought pure neem oil through amazon, the prices vary a lot, so compare. As any vegetable oil it should be stored in a cool and a dark place. If stored in a fridge, it flocks, so it has to turn liquid again before using. The water for the solution should be min.15 degrees warm. It needs an emulsifier, will otherwise not mix with water, some liquid soap will do, but there is a special product called Rimulgan sold for that purpose. The solution against aphids, mealybugs etc. would be 1-2% neem oil to water. Use the solution in 4 hours, do not store. Spray only in the evening and don't use any sulfur-based fungicides at the same time to avoid leaves to burn. Neem oil functions as an insecticide and a fungicide. Usually 2-3 sprayings in 7-10 day intervals should be enough. If you have solution left, you can pour some on on the roots, mealybugs for example might be in the earth as well. And you can pour some in water tanks agains mosquitos. 2% neem oil in coconut oil will make a mosquito repellent for humans, that should function for 12 hours. There are many more ways to use neem oil and there are products, that already contain the emulsifier.