How to use and what effect of the acne treatmen serum?

For the acne skin, I want to ask what is the use method and effect of acne cream or acne treatment serum? 

Generally speaking, the use of acne treatment serum should be the third step of women's skin care, that is, after the use of cleanser, toner, then use acne cream. Acne treatment serum not only has a good role in skin care and whitening, but also promotes pore contraction and replenishes collagen. At the same time, the more obvious role is to remove acne and prevent the generation of spots. Because it contains rich plant extracts, such as green tea essential oil, houttuynia extract, scutellaria root extract and so on