Sorry, but we cannot advise you on how to get a free computer--especially since we have no idea where you are. If you were asking about the area where I personally live, I would actually know, but the U.S. is a very big place. You could look into getting a friend or relative to loan you the use of theirs. Or you could prepare your tax return on paper forms by hand to mail in.
Instructions for Form 1040 (HTML)
The tax forms are different for 2018 and beyond since the new tax laws went into effect. Everyone gets a "postcard size" Form 1040 that only goes to line 23. In addition, there are six possible extra pages called "schedules" that may be included as part of the tax return that you prepare and file.
https://www.irs.gov/pub/irs-pdf/f1040.pdf
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
**Disclaimer: Every effort has been made to offer the most correct information possible. The poster disclaims any legal responsibility for the accuracy of the information that is contained in this post.**
