There are four levels of protein structure. The short answer is these levels of structure give a protein its overall shape. The job (function) of the protein depends on its shape.
The video below discusses the topic of protein structure.
1. The sequence (order) of amino acids in a protein will determine the shape of the protein
2. The job of a protein is determined by its shape
3. A change in shape of a protein will cause its functionality to be altered or lost.
5. Factors which can change the shape of a protein are changes in temperature (heat) or changes in pH level (acidic or basic).
Video from: Noel Pauller
Hope this helps!