Step 1: Identify constants $ \color{blue}{ b }$ and $\color{red}{ c }$. ( $ \color{blue}{ b }$ is a number in front of the $ x $ term and $ \color{red}{ c } $ is a constant). In our case:

$$ \color{blue}{ b = 26 } ~ \text{ and } ~ \color{red}{ c = 168 }$$

Now we must discover two numbers that sum up to $ \color{blue}{ 26 } $ and multiply to $ \color{red}{ 168 } $.

Step 2: Find out pairs of numbers with a product of $\color{red}{ c = 168 }$.

PRODUCT = 168
1     168	-1     -168
2     84	-2     -84
3     56	-3     -56
4     42	-4     -42
6     28	-6     -28
7     24	-7     -24
8     21	-8     -21
12     14	-12     -14

Step 3: Find out which pair sums up to $\color{blue}{ b = 26 }$

PRODUCT = 168 and SUM = 26
1     168	-1     -168
2     84	-2     -84
3     56	-3     -56
4     42	-4     -42
6     28	-6     -28
7     24	-7     -24
8     21	-8     -21
12     14	-12     -14

Step 4: Put 12 and 14 into placeholders to get factored form.

$$ \begin{aligned} x^{2}+26x+168 & = (x + \color{orangered}{\square} )(x + \color{orangered}{\square}) \\ x^{2}+26x+168 & = (x + 12)(x + 14) \end{aligned} $$

Polynomial Factoring Calculator