How do I go about filing back taxes... And not having all the w-2 forms?

[DoninGA]

You can use TurboTax to file for tax years 2018 thru 2016 by purchasing, downloading and installing on a personal computer one of the desktop editions for each tax year required from this website - https://turbotax.intuit.com/personal-taxes/past-years-products/

Prior year tax returns can only be printed and mailed, they cannot be e-filed.

If you cannot obtain the W-2 from your employer, then for a fee you can get a complete copy of a W-2 from the Social Security Administration - https://faq.ssa.gov/en-us/Topic/article/KA-02501

You can get a free Wage and Income transcript from the IRS - https://www.irs.gov/individuals/get-transcript

[xmasbaby0]

Not having your W-2's is a problem.  You should make every effort to obtain those from the employers who issued them--even if you have to beg.  You need them.  The other thing you can do is get a wage and income transcript from the IRS which will show the income reported to the IRS by the employers  but it will only show federal information--no state info  -- so if you need to prepare state returns the transcript will not help with that.

You can get a free transcript from the IRS:   

https://www.irs.gov/individuals/get-transcript

As for preparing the returns--you can use desktop TurboTax software for years 2016 through 2018.  It has to be downloaded to a full PC or Mac--not a mobile device.  And the returns must be printed, signed and mailed--they cannot be e-filed.