To determine the value of \( h \) in the function \( f(x) = x + h \) that describes the translation of the point from \( (5, 6) \) to \( (3, 6) \), we focus on the x-coordinates.
The original x-coordinate is 5 and the new x-coordinate after the translation is 3. The function \( f(x) \) describes how the x-coordinate changes, so we can express it as:
\[ f(5) = 5 + h \]
We want this to equal the new x-coordinate:
\[ f(5) = 3 \]
Setting the equation gives us:
\[ 5 + h = 3 \]
To solve for \( h \):
\[ h = 3 - 5 \] \[ h = -2 \]
Thus, the value of \( h \) is \(\boxed{-2}\).