Simplifying
x3 + 5x2 + 6x

Reorder the terms:
6x + 5x2 + x3

Factor out the Greatest Common Factor (GCF), 'x'.
x(6 + 5x + x2)

Factor a trinomial.
x((3 + x)(2 + x))

Final result:
x(3 + x)(2 + x)