How to find the output signal of a filter using state space matrices?
We don't know anything about your system, but general rule is:

$$\begin{array}
&amp;y[n] &amp;= \mathbf{C}x[n] + \mathbf{D}u[n]\\
x[n+1] &amp;=\mathbf{A}x[n] + \mathbf{B}u[n] \\
\end{array}$$

Where $u[n]$ is the input signal value, $x[n]$ is state vector value at a given point in time, and $y[n]$ is obviously the output. 

What you need to do is to: 


Initialize the initial state $x[0]$ to some arbitrary value (usually vector of zeros).
Run the calculation by consequently calculating values of $y[n]$ and $x[n+1]$ to be used in the next step. 


Speaking Matlab'ish (not tested, cause I am in travel, but given all informations its extremely easy to figure out what is going on):

b = [0 2 3];
a = [1 0.4 1];
[A,B,C,D] = tf2ss(b,a);

x_0 = zeros(size(A,1), 1); % Initial state
N = 9;
u = randn(1, N); % Some input signal
y = zeros(N, 1); % Output signal

x = u_0;
for n=1:N-1
  y(n) = C*x + D*u(n); % System output
  x = A*x + B*u(n);    % Transition
end