The work area is the main area visible in the AddUp window. It is where calculations are done, result are shown and errors are reported. This space behaves more or less like a regular Windows text editor.
Try a simple addition in the work area. Type in 1+2 then press the Enter key.
1+2 = 3
Expressions you provide are calculated when you press Enter. The result is given twice: once at the end of the line following an equal sign, and once again two lines below. The second copy lets you continue to operate on the result of the last calculation without having to re-enter or copy it from the line above. It appears on a new line of its own with the caret next to it, ready to be reused. If you do not need this second copy of the result, press the Esc key to remove it.
If you press the Esc key repeatedly you can undo successive steps of the last calculation, back to the original expression. You can then modify the expression and repeat the calculation if desired. You could also use the arrow keys to move the caret back to the original expression, modify it and press Enter again to obtain a new result.
Occasionally you will make a mistake when entering an expression. Enter a parenthesized expression, but purposely introduce an error with the parentheses so that they are incorrectly balanced: type in (1+2)*3) and press Enter.
(1+2)*3) = Error (parentheses)
The error is reported in red and the caret moves next to the problem: there is a superfluous closing parenthesis. Delete the redundant parenthesis and press Enter again (no need to erase the error message). The correct result is displayed once the mistake is fixed:
(1+2)*3 = 9
(For conciseness, the second result will no longer be shown in later examples.)
You see how the Enter key evaluates the expression on the current line. But if you need to use it normally instead of trying to evaluate the content of the current line then hold down the Ctrl key on your keyboard as you press Enter. This allows you to either break a long line in two or skip to the next line without evaluating it. You can annotate your work using regular text and then press Ctrl-Enter to advance to the next line without making AddUp try to evaluate the text.