The hard part is that you want n to go from 0 to N-1, but MATLAB wants n to go from 1 to N. To get around this do everything in terms of m = n+1 and then subtract it off in the end ...
m = 1;
N = 10;
x = zeros(N, 1);
x(m) = 1;
x(m+1) = -1;
x(m+2) = -1;
h = zeros(N, 1);
h(m) = 1;
h(m+1) = 2;
h(m+2) = 3;
h(m+4) = -1;
figure;
subplot(2,2,1);
stem((1:N)-m, x);
title('x');
subplot(2,2,2);
stem((1:N)-m, h)
title('h');
subplot(2,2,3:4);
stem((1:(2*N-1))-m, conv(x,h));
