If I’m 18 years old how can I file my taxes if this is my first time

You can start a tax return using the online Free edition.  Just click on the button labeled File for $0 and sign onto your account or create an account - https://turbotax.intuit.com/personal-taxes/online/

Then follow the interview for entering your personal information and your tax information.

If you are claimed as a dependent on someone else's tax return make sure that you indicate you are a dependent in the My Info section of the program when you are entering your personal information.

If you were an employee then you should be receiving a form W-2 for 2019 on or before January 31, 2020 from your employer.  The W-2 must be entered on your tax return in the Wages and Income section of the program.

Edit answer for January 31, 2020.

Additionally, after your tax return has been completed and has passed the Review section of the program you will be taken to the File section.  This is where you indicate whether you want to either e-file or print the return for mailing.  Choose the e-file option.

You complete your tax return by finishing all 3 Steps in the File section. In Step 3, to e-file your tax return, you must click on the large Orange button labeled "

Transmit my returns now

After completing the File section and e-filing your tax return you will receive two emails from TurboTax. The first email when your tax return was transmitted and the second email when the tax return has either been accepted or rejected.