1. Problem: draw the sets example for $a$ and $b$. 2. Use one concrete example: $a=\{1,2,3\}$ and $b=\{3,4\}$. 3. In a Venn diagram, put $1$ and $2$ only in $a$, put $4$ only in $b$, and put $3$ in the overlap. 4. So the regions are $a\text{-only}=\{1,2\}$, $a\cap b=\{3\}$, and $b\text{-only}=\{4\}$. 5. The union is $a\cup b=\{1,2,3,4\}$.