Retirement tax questions

so here is the problem (that I subsequently learned)...i apparently screwed up last year and answered a question incorrectly. last year's 1099R has a number in the GROSS DISTRIBUTION box (#1) a smaller number in the TAXABLE AMOUNT box (#2a).  It appears that whatever I did last year I DID NOT go thru a series of questions regarding the original start date and plan cost etc or electing simplified method. Subsequently the amount that was used was the exact amount appearing in the TAXABLE AMOUNT box (#2a).  So when I did my taxes this year, there wasn't anything in the "TAX-FREE Amount Previously Recovered" box.  I also had/have trouble answering the "Describe the Taxable Amount" page. I was confused when it asked to either select "yes, the taxable annuity amount was used as the taxable amount" or "no, a different amount was taxable." I didn't know what the difference was between the "taxable annuity amount" and the "taxable amount".  Additionally, i was confused on regarding the sentence on the "Why we used simplified method to compute the taxable amount" page, i.e. "The taxable amount is $xxxx. We'll use this amount on your return, rather than the gross annuity amount shown on Form CSA/CSF 1099-R." What number are they referring to when they say "gross annuity amount"?