Estimated final cost is what's spent plus the estimate to complete. The estimate starts as whatever is left of the budget; click a line to change it. Variance is the budget less the estimated final cost: under budget is positive.
No budget yet
Budget-to-actuals compares what you've spent, from the expense log, against the budget, line by line: what's spent, what's left to spend, the estimated final cost, and whether each line is over or under. Build the budget in the budget tool, log spending in the expense log, then open the project here.
Where it stands
Counts expenses up to this date. Leave it empty for all of them.
Over budget
Not in the budget
Expenses with no budget account, or an account the budget doesn't have. Give them an account in the expense log.
A cost report: the totals, then every account and line.