Can you tell me how to understanding mental illenss and mental retardation?

Very different: Mental illness and mental retardation are two very different things and not neccesarily related. If you have questions about either, you could ask your physician, you could read a good book on the subjects, or you could talk to people who have these conditions. Doctors who treat these conditions are very helpful, and there are many in your area at Illinois Neurologic Institute in Peoria.

Mental illness: is a condition were a person with or without intellectual disability starts to function or think abnormally without a medical illness while Intellectual Disability is where people have functioning and intellectual capacity lower than their physical age and they usually score low on their IQ test. Majority especially profound type will be unable to function or carry out financial transactions