If you want to review the tax return before filing, there are two ways to do it:
First, when you're logged into your return, go to the upper margin of the screen and click on My Account. Then from the dropdown box select Tools. When the Tool Center window opens, click on the first item in the list of Other Helpful Links, View Tax Summary. When the summary page loads, look up above the summary and click on Preview My 1040. That will show you the two-page 1040 form for you to review.
Second, if you want to see all the various forms & schedules that are included with the 1040, then you'll need to pay first (you won't have to file yet). Once you've made payment, then again go to My Account, click on Print Center from the dropdown box, and you'll be able to view/print/download the entire tax return, including all forms & schedules.