Am I able to file my 2018 and 2019 taxes for free online?

Yes, you can file 2019 using the online version of TurboTax.  For 2018 you will need to purchase the desktop version of TurboTax for 2018 to file a return. 

Here is a link to TurboTax Free Edition.  You have to meet certain parameters to qualify.

If you do not meet the parameters, there will be a charge for additional forms you may need to use to file your return. You can use this link to file your return  TurboTax.

I bought turbo tax 18 but it want let me efile my taxes. My taxes are done i just need to efile them please help

I have already done that paying twice is unfare

What are you paying twice for?  Did you already pay for 2018 online last year?

It is too late to efile 2018.  You have to print and mail prior year returns.  And Online is only good for 2019 now.