Can someone please explain to me when/what i need to do to claim my tax return and request for a child support.

I am currently an employee since Jun-2016 who pays the taxes as it goes from my company to the IRD. What I recently came to know that i have to apply for tax return. when i googled it, i see that i can claim it through agencies which they take fees to handle the procedure.

Do you know a direct link that i can file this request by myself?

Can i claim back the tax return for the past two years, or it is gone away since i did not apply?

My child was born on Jul-2016, and i did not claim any child support as i did not know how things are going here.

Do you know how can i claim that back as well?

Please note that I also pay more than half of my income as a rent while the rest is gone for basic needs. Not sure if there is something else i need to know or i can ask the work and income for?

Any advice is much appreciated