please explain to me how I work out problems such as "-2-3" to get the correct answer and show the same on a number line

Answer 1

If you owe your brother $2 and then borrow another $3 from him -- how much do you owe him?

This number line should help you.

http://img.brothersoft.com/screenshots/softimage/n/number_line-1363-1.jpeg

Answer 2

Right. Always think of negative numbers as money you owe and positive numbers as money you have. I believe that's the easiest way to evaluate those expressions.