If I need to request an extension on filing federal and state taxes for 2018, do I need to do the whole process, as if I'm filing today?

[IreneS]

I'm not sure what you mean by the "whole process," but if you are going to file an extension you need to do it today (Monday) before midnight in your time zone.  You will need to estimate what your tax bill will be for 2018.  [It doesn't have to be exact.]

To file an extension, please follow these steps:

TurboTax Online

1. In your return, type extension in the Search box at the top of the page.
2. Click the Jump to extension link
3. On the Need More Time to File Your Return? screen, click on the blue box, Start Easy Extension.
4. Click Continue in the pop-up window.
5. On the next screen click the File an Extension box.
6. Continue through the screens, entering the requested information.

TurboTax CD/Download

 You cannot e-file an extension from the TurboTax CD/Download editions.  You can print out Form 4868 and mail it in. To do this

1. Click Federal Taxes >  Other Tax Situations
2. Under Other Tax Forms, click the Start/Update box next to File an Extension.
3. On the next screen, mark the Yes radio button and click Continue.
4. Continue through the screens until you reach the screen, Your Extension Results.  Click the Print Extension box.

You can also go to the TurboTax Easy Extension website to file your extension online:

1. Go to:  https://turbotax.intuit.com/irs-tax-extensions/
2. Click the File a Free Extension box. 

You will be asked to sign in with your TurboTax Online ID.  If you don't have one, click Create an Account at the bottom of the sign in screen.

Please check the FAQ below for information on extensions for your state:

https://ttlc.intuit.com/replies/3300227

[fanfare]

when you request an extension you're expected to pay the full balance.
go to www.irs.gov/payments and "Make a payment"
select Reason: Extension

Since you don't know that balance yet you need to overestimate generously to avoid penalty.
You'll get it back when you file.

Make a note of your payment  amount so you can claim credit for that when you file.