Hi Sbia,
Yes mix it with the shampoo and apply it to the hair.
NO your hair should not feel greasy, it will feel dry as your washing your hair but then once you blow dry your hair after should come out nice and shiny and thick. It also depends on your hair type. My is naturally dry so everything feels dry for me, buts its made my hair shiny and soft. It doesnt affect my partners oily hair though.
You dont use conditioner because it will thin the hair again. Soon you will get used to not using conditioner as it thins the hair and makes it more prone to breakage. Whilst the shampoo makes the hair strong. I advise only to use a conditioning treatment once every two weeks so as to keep the hair manageable, but not everyday.