Filling a Sched 4 on 2017 Corp return and can't figure how to fill in losses for past yearsThere is no data field to enter values for "Current year loss net of carryback"

I need to record accumulating corporate losses each year from 2006 to 2017 (with the exception of 2007 with 0). However, without an input field for "current year loss net of carryback" I cannot seem to enter the yearly losses to accumulate forward.

I also don't understand what the difference between "balance at end of previous year" and "balance at beginning of tax year" is ..since nothing transpires between the end of one year and the beginning of the next. Very confusing, and hardly an easy walk through for a first time novice.

Note: this is for a CORPORATE return. All FAQs seem to relate only to personal taxes.