How can I see the forms as I'm filling in the information? The menu bar at the left offers only TAX HOME and DOCUMENTS -- no other choices.

You cannot see the forms.   Online software does not have Forms mode.  That is a feature of desktop software.  With online, you can only preview your 1040 and the Schedules 1, 2 or 3 before you pay your fees.

https://ttlc.intuit.com/turbotax-support/en-us/help-article/tax-return/preview-turbotax-online-return-filing/L77WCkvnu_US_en_US?uid=m681fkhr

Pay the preparation fee and register -- then you can see your entire return.
Visit the Print Center to get the ball rolling.
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Always print a copy of your completed tax return for your records, and review it carefully before e-Filing.
You will need it if you are audited by the IRS, to contact the IRS, or to amend if a TurboTax update changes your return or for any other reason,

AND, to find your AGI next year.

@dlw1001