What are the medical concerns as well as benefits of high and low levels of LDL and HDL?

What are the medical concerns as well as benefits of high and low levels of LDL and HDL?

What is Cholesterol?
To which class of biological molecules does cholesterol belong?
What is the difference between HDL and LDL?
What are the medical concerns as well as benefits of high and low levels of LDL and HDL?
(Minimum length of paper 500 words.) Papers need to be referenced and follow APA