I have the problem below I understand how convolution works but I don't understand where this x has come from and how to use it. Do I assume it is x(t)?

$\displaystyle s(t) = 0$ (for t <= 0)

$\displaystyle s(t) = 1$ (for t > 0)

convolve $\displaystyle y = h * x$

where $\displaystyle h(t) = a^t s(t)$ for some $\displaystyle a \Re$ and u = s

How do I solve this?