Most of the seniors understand about filling out the tax form on social security income.

The question is: will IRS mail out the tax package including the mailing envelop.

Or must the seniors dowload the a blank 1040a, and use a regular mailing envelop.

I don't believe that the IRS will automatically send out a tax form. They typically only send forms to people that have previously filed via paper. For the internet-challenged they can always call the IRS or get a form at their local post office.