We need more information about what you are having trouble with.
The Form 1040 is the U.S. Individual Income Tax Return that you complete and send to the IRS.
When using the TurboTax software you are completing the Form 1040.
Why do you ask?
You don't "enter a 1040". Everything you enter is to fill out the 1040 return. You enter your personal info, W2 and any 1099 you get. Did you get a form you are trying to enter? Or what are you trying to do with a 1040?
A 1040 is the tax return form you prepare here to send to the IRS. If you start entering data in this software you are preparing a Form 1040. Please look at it so you will know what you are sending to the IRS:
PREVIEW 1040
https://ttlc.intuit.com/questions/1901539-how-do-i-preview-my-turbotax-online-return-before-filing
Click on Tax Tools on the left side of the screen. Click on Tools. Click on View Tax Summary. Click on Preview my 1040 on the left side of the screen.