To find f(x + h) for the function f(x) = 10 - x², substitute (x + h) into the function, resulting in f(x + h) = 10 - (x + h)². This expands to f(x + h) = 10 - (x² + 2xh + h²). The discussion also highlights that evaluating f at specific points, like f(2) and f(√10), demonstrates how to find function values and identify roots. The key takeaway is the straightforward substitution method for evaluating functions at different inputs. Understanding this process is essential for solving similar problems in algebra.