Well you can't really "access" it in the sense of seeing it as a form and entering numbers into it. That's reserved for the desktop versions.
If you need to get entries onto Schedule D then the most common path is to use the "Stocks, Mutual Funds, Bonds, Other" interview and enter your security trades that way. Those entries get place on Form 8949 and summary numbers flow off them and onto Schedule D. There are other ways to get numbers onto Schedule D, but they all involve the appropriate interview, e.g., the "Schedule K-1" interview.
Tom Young