It is too late to get an extension. Extensions had to be filed by April 15 and only gives you to Oct 15 to file. And Efiling is now closed. You can mail in a 2018 return.
To do a prior year return you have to buy the Desktop program here,
https://turbotax.intuit.com/personal-taxes/past-years-products/
You will need a full Windows or Mac to install it on.
Or If you have a simple return You can fill out the blank forms for free.
Here is the new IRS 2018 Form 1040
https://www.irs.gov/pub/irs-pdf/f1040.pdf
And instructions https://www.irs.gov/pub/irs-pdf/i1040gi.pdf
2018 Tax and EIC Tables https://www.irs.gov/pub/irs-pdf/i1040tt.pdf
IRS 2018 Schedules 1 thru 6 (only if needed)
https://www.irs.gov/pub/irs-pdf/f1040s1.pdf
https://www.irs.gov/pub/irs-pdf/f1040s2.pdf
https://www.irs.gov/pub/irs-pdf/f1040s3.pdf
https://www.irs.gov/pub/irs-pdf/f1040s4.pdf
https://www.irs.gov/pub/irs-pdf/f1040s5.pdf
https://www.irs.gov/pub/irs-pdf/f1040s6.pdf
