Return of income

In village area there are so many people not filling return of income. They have also taxable income about 3 to 4 lakhs from various source. Reason for not filling of return of income is they have not knowledge of it. Such type of people are not maintaining any accounts. > is there any problem for them in futer if not files return of income ? > will income tax department take any action against them ? >what should they to do for filling return of income?