It is too late to file for refunds for tax years 2012 - 2015 ... so start with the open tax years first.
You can only buy the last 3 years, so 2015-2017 here, https://turbotax.intuit.com/personal-taxes/past-years-products/
You have to print and mail prior year returns. Send each year in a separate envelope.
Then for older returns you need to go somewhere local or get the blank forms from the IRS and state. I have links to some.
Like Here are some blank forms & instructions for 2014
1040 https://www.irs.gov/pub/irs-prior/f1040--2014.pdf
Instructions https://www.irs.gov/pub/irs-prior/i1040gi--2014.pdf
1040A https://www.irs.gov/pub/irs-prior/f1040a--2014.pdf
Instructions https://www.irs.gov/pub/irs-prior/i1040a--2014.pdf
1040EZ https://www.irs.gov/pub/irs-prior/f1040ez--2014.pdf
Instructions https://www.irs.gov/pub/irs-prior/i1040ez--2014.pdf
2014 Tax Tables https://www.irs.gov/pub/irs-prior/i1040tt--2014.pdf
Publication 17 Tax Guide for 2014 https://www.irs.gov/pub/irs-prior/p17--2014.pdf
Don’t forget your state. And you will have to print and mail your returns. So be sure to attach copies of your W2s and any 1099s that have withholding on them. You have to mail federal and state in separate envelopes because they go to different places. Get a tracking number from the post office when you mail them for proof of filing.