1. The problem is to understand how to work with an addition sign in math expressions. 2. The addition sign "+" means to combine or add two numbers or expressions. 3. For example, if you have $3 + 5$, you add 3 and 5 together. 4. Calculate $3 + 5 = 8$. 5. So, the addition sign tells you to sum the values on either side. 6. This applies to variables as well, for example, $x + y$ means the sum of $x$ and $y$. 7. In summary, the addition sign is used to add numbers or expressions together to get their total.