We have indeterminateness of type
0/0,
i.e. limit for the numerator is
$$\lim_{x \to 0^+}\left(\left(x + 1\right)^{a} - 1\right) = 0$$
and limit for the denominator is
$$\lim_{x \to 0^+} x = 0$$
Let's take derivatives of the numerator and denominator until we eliminate indeterninateness.
$$\lim_{x \to 0^+}\left(\frac{\left(x + 1\right)^{a} - 1}{x}\right)$$
=
$$\lim_{x \to 0^+}\left(\frac{\left(x + 1\right)^{a} - 1}{x}\right)$$
=
$$a$$
It can be seen that we have applied Lopital's rule (we have taken derivatives with respect to the numerator and denominator) 0 time(s)