So the question is asking how much total paint was used, if he used 2/3 of a 1/2 can of paint. Whenever the word "of" is used with fractions, multiplication can be used to find the answer. To multiply fractions, multiply the numerator by the other numerator, and the denominator by the other denominator:
(1/2)x(2/3)=2/6
2/6 reduces to 1/3
So Titus used 1/3 of the original can of paint.