Non filing of income tax return

Dear All,

I am a salaried employee with no other income than salary. I have not filed my ITR for any previous years because TDS was deducted by my employer and I didn't realised that I have to file ITR but now I have received a notice asking to submit my response for non filing of ITR, in the compliance portal online. Please suggest me what response should I submit and what consequences are going to be and is there any reason to be afraid of?

Thanks to All