I entered "census" in the "What kind of source do you want to cite?" field above. Note that I could have selected "census records" from the "choose the type of record from this list."
2) I clicked on "Search" and had to select from a very long list of census records. Eventually, I found the 1940 U.S. Census with digital images:
3) I clicked on the "1940 > Census records > United States > Federal census records > 1940 population schedule > Online images" line and clicked on the "Go" button. The "Step 2. Fill in the fields below" page opened:
In the "Source Info" tab, I added information for the Source list name, state, county, website title, website URL, publish date, and format, as shown above. Note that the database title ("1940 U.S. census"), the publisher (National Archives and Records Administration") and the Series ("T627") are already filled in.
I could have added information in the "Text/Comments," "Repository," "Multimedia" and "Override" tabs also.
4) I clicked on the "Save" button and the "Edit the Source Detail" screen opened. Here, I added information for the City, Roll Number, Enumeration District, Sheet, Page, and Household Number.
The screen above shows the information that I entered into the fields.
5) I clicked on the Save button, and I was back to the "Assigned Sources" screen, and the Footnote/Endnote Citation, the Subsequent Citation and the Bibliography in the lower part of the screen:
UPDATE 1:50 p.m.: I just looked at my Legacy database source citations, with the database imported from RootsMagic, and many census source citations are truncated as shown above because the Citation Detail is too long for the allowable field. I have hundreds of source citations longer than 255 characters in my RootsMagic database.