The premise
given factor (x-a) to f(x)=Bx^2+Cx+D,
The pink arrow means multiply a by whatever the difference of the previous column's value was (it's subtraction).
You start out with taking B and putting it in the difference row, so the next column will be C-aB. The next column should be D-a(C-aB), and so on. This applies to all polynomial equations.
Also, you CANNOT miss a term, so if you have something like 3x^5+8x^3-2x^2 you would have to write in 0s for the missing terms...
like this \rightarrow3x^5+0x^4+8x^3-2x^2+0x-0
Your result should have all the powers of x shifted down one degree, so a polynomial beginning with x^5 would have a quotient beginning with x^4.
If the last column does not get you a 0 as the result, then it will be the remainder, which you put over the factor you divided by, \frac(\text(remainder))(x-a)
Actual calculation
14x^2-34\leftrightarrow14x^2+0x-34
dividing by (x+4); from (x-a) form that means a=-4
So we have the synthetic division set up:
-4 | 14 0 -34
----.--------.------.
\color{white}{abc}14
-4 | 14 \color{white}{a} 0 \color{white}{abc}-34
-\color{white}{abc}(-56) \color{white}{a}224
---.----------.----------.
\color{white}{abc}14\color{white}{ab}56\color{white}{abc}258
We get 14x-56+\frac{258}{x-4}