To solve the expression $\frac{2}{3} + \frac{3}{9}$, we need to first find a common denominator.

Step-by-step:

1. The denominators are 3 and 9. The least common denominator (LCD) is 9.
2. Rewrite $\frac{2}{3}$ with the denominator 9: $\frac{2}{3} = \frac{6}{9}$
3. Now add the fractions: $\frac{6}{9} + \frac{3}{9} = \frac{6+3}{9} = \frac{9}{9} = 1$

So, $\frac{2}{3} + \frac{3}{9} = 1$.

Would you like more details on any part of the process? Here are five related questions you might find useful:

1. What is the general process for adding fractions with different denominators?
2. How do you find the least common denominator (LCD)?
3. Can you explain how to simplify fractions?
4. What is the difference between proper and improper fractions?
5. How can fractions be converted into decimals?

Tip: When adding fractions, always simplify the fractions first if possible—it makes calculations easier!