How do I know if I paid federal taxes in 2018 or not

If you had a job in 2018, you paid federal taxes.  If your question is whether you received a defund or owed money to the irs at the end of the year, you need to find your copy of last years tax return.

If you need a copy of your last years' return and you filed with TurboTax, here's how you can access it: https://ttlc.intuit.com/community/prior-year-return/help/how-do-i-access-my-prior-year-return/01/27010