Oook don't worry, so at 1st will start to draw still life to know how we can make realistic paintings but we'll start with one item such as an Apple or or an Orange or even a Ball , before you draw it you have starve on it a lot and watch how the light and shadow come on it , i see you can draw an Apple but you just need some practice to use a Pencil and shade varefully and soft.... so there are ways of shades..

you have practice the shade firts, create 5 small sqaures or more then choose one way of shades and try to shade them from light to dark and 2nd time from dark to light .