A withdrawal in 2019, not a Loan, from a 401(k) will be reported to you on a Form 1099-R by the plan administrator. You will receive the 1099-R in January 2020. The taxable amount of the withdrawal is entered on your federal tax return and taxed at your current tax rate. Any federal taxes withheld will be entered on your federal tax return as a tax payment. If you are under the age of 59 1/2 you will be assessed a 10% early withdrawal penalty on the withdrawal.
A withdrawal versus a Loan is not paid back to the 401(k) account.
