Do I have to use Turbotax both for Federal and state tax together? How could I only use Turbotax for Federal tax

No, you can just file the federal return. Skip the state section and move on to review and then file.

I actually already filled out the state tax. In that case, could I skip the state tax? It was free using Turbox tax for state tax last year, somehow it charged, so I want to use another free tool to prepare state tax. How could I skip now ( I saw that I had to pay both together )

You can file just your federal return in TurboTax.

 

If you already started a state return, you can delete it as long as you haven't paid for it yet (or registered your free version with the state attached). 

1. Sign in and open a section of your return
2. From the menu, select State and then select Continue on the Let's get your state taxes done right screen
3. On the Status of your state returns screen, select Delete next to your state, then answer Yes

When you go through the File section of TurboTax, you can choose which returns to file. 

I did try that. I only see "state tax" and if I continue with that, I didn't see delete. 

You will not be able to delete your state tax return if you paid for TurboTax Online. You can only clear your state return and start over. 

 

In the File section, you can change your state return to file later.

 

If you've already paid for your state, consider filing it. To check whether you bought state, 

 

1. Tap Tax Tools in the left column
2. Then Tools
3. In "Tools Center" choose My Fees (the bottom right box)