Each column must add up to 13. Fill in the missing numbers. Below draw them in a different way.

The sum of the known numbers in the first column is $1 + 1 + 1 = 3$.
To reach a total of 13, the missing number is:

$$13 - 3 = 10$$

The sum of the known numbers in the second column is $2 + 3 = 5$.
To reach a total of 13, the missing number is:

$$13 - 5 = 8$$

The sum of the known numbers in the third column is $6 + 2 = 8$.
To reach a total of 13, the missing number is:

$$13 - 8 = 5$$

The completed table is:

$$\begin{bmatrix} 1 & 2 & 6 \\ 1 & \boxed{8} & \boxed{5} \\ 1 & 3 & 2 \\ \hline 13 & 13 & 13 \end{bmatrix}$$