The GCD of given numbers is 3.
Step 1 : Find prime factorization of each number.
$$\begin{aligned}24 =& 2\cdot2\cdot2\cdot3\\[8pt]63 =& 3\cdot3\cdot7\\[8pt]\end{aligned}$$(view steps on how to factor 24 and 63. )
Step 2 : Put a box around factors that are common for all numbers:
$$\begin{aligned}24 =& 2\cdot2\cdot2\cdot\color{blue}{\boxed{3}}\\[8pt]63 =& \color{blue}{\boxed{3}}\cdot3\cdot7\\[8pt]\end{aligned}$$Step 3 : Multiply the boxed numbers together:
$$ GCD = 3 $$This solution can be visualized using a Venn diagram.
The GCD equals the product of the numbers at the intersection.