I was employed majority of 2020 and started a sole-proprietorship in August. They both obviously use my SSN. Do I file taxes separately, one after the other?

[vismaad]

Is it possible to file them together?

[RayW7]

You would file for both types of employment on the same return.

I assume you received a W2 from you first job.  For that income you will enter it in TurboTax following the questions for W2 income, in the Personal Income Section.

The remaining income would be reported on a Schedule C.  To enter that income go to the Business Income and Expense section and enter your earnings and any related expenses.

You may want to upgrade to the Home and Business version if you do not have it.  TurboTax will guide you through this. 

[vismaad]

Thank you very much Ray. concern was deciding which "plan" to choose.