This area shows you the current values of any locally defined variables. As you step through the code, these values will update immediately so you can see what is happening. Often, models may not behave correctly because variables in code are not what they are expected to be. This window allows you to see exactly what the variables are.
Alternatively, you can mouse over variables in the Code Edit window to see their current value.
Keep in mind, the yellow arrow is pointing to the next line to be executed, so if a new variable is being initialized, you will not be able to see its value until after that line has been executed.