World Mental Illness Awareness

So today the 5th July marks the start to World Mental Illness awareness month. We see and face many situations where mental illness is around us all the time. Be it in our families, in our communities or just in a public space.
However what is mental illness?
How do we determine who suffers from it?
How can one cure it?
What do you do when you come over such a situation?
These are the questions that lingers.